Banaras Khan / AFP - Getty Images, file

Pakistani volunteers carry the coffin of British aid worker Khalil Dale, before handing it over to Red Cross officials in Quetta on April 30.

PESHAWAR, Pakistan -- The International Committee of the Red Cross (ICRC) said late Tuesday it was halting most aid programs in Pakistan due to fears over deteriorating security – a concern underscored early Wednesday when 19 soldiers and militants were killed in a clash at a military checkpoint.

The independent global aid agency, which rarely suspends its operations even in war zones, has worked in the country since the end of British colonial rule in 1947 - but was shaken by the discovery in April of the beheaded body of British doctor Khalil Rasjed Dale, one of its health workers.

It said it would carry on working in the country "but on a reduced scale," having already suspended operations in three of Pakistan's four provinces in May pending a security assessment.

Paul Castella, head of the ICRC delegation in Islamabad, said in a statement: "We are ready to continue helping people in need, such as the wounded and the physically disabled, provided working conditions for our staff are adequate. In the coming weeks, we will coordinate with the Pakistani authorities the resumption of health services as conditions permit, in particular the re-opening of our surgical hospital in Peshawar, which closed down after the murder of our colleague."

Aid workers become targets as Pakistan faces new humanitarian crisis

The statement said the ICRC's partnership with the Pakistan Red Crescent Society and support for physical rehabilitation services, notably in Peshawar and Muzaffarabad, will continue, as will the assistance provided by the ICRC for families seeking to restore and maintain contact with Pakistanis detained abroad.

The killing of an ICRC official in Quetta had seriously worried staff members of the organization about their security in Pakistan, particularly in the Khyber Pakhtunkhwa and Balochistan. Dale, who converted to Islam, ran a health program in Quetta when he was kidnapped on January 5 while going home from work.

Slideshow: Pakistan: A nation in turmoil

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Images of daily life, political pursuits, religious rites and deadly violence.

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His body was found on April 29 with a note that said the ICRC’s failure to pay ransom was the reason for his killing.

Red Cross doctor found beheaded in Pakistan

Dale was the third foreigner beheaded in Pakistan, after Wall Street Journal reporter Daniel Pearl in 2002 and Polish geologist Piotr Stanczak in 2009.

The Pakistan Taliban have been fighting a bloody insurgency against the Pakistani state since the group was formed 2007, Reuters reported. It is close to al-Qaida and it claimed credit for a failed car bomb attempt in New York's Times Square in May 2010. 

Ex-ambassador: US, Pakistan should 'divorce'

Meanwhile at least 19 people - nine Pakistan Army soldiers and 10 militants – were killed and 16 others injured in clashes between the Pakistani security forces and militants at the remote mountainous Ghatsar area of Tiarza, South Waziristan, on Wednesday.

Senior military officials said dozens of militants had attacked military checkpoints located in the mountains on Tuesday night that led to heavy fighting in the area.

Pakistani Christians live in fear after girl's blasphemy arrest

"The militants attacked our checkpoints with heavy weapons last night,” said a senior Pakistani military official based in Wana, the main administrative city of South Waziristan tribal region.

“The soldiers retaliated and engaged the militants. Fighting is still going on in which nine soldiers lost their lives. The security forces had killed 10 militants and injured several others in the overnight clashes.”

South Waziristan, which is one of Pakistan's seven autonomous tribal regions, is mostly controlled by Pakistani militants, Afghan Taliban and al-Qaeda operatives making it difficult for the government and its armed forces to carry out their responsibilities.

Reuters contributed to this report.

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Shaam News Network via Reuters

Syrians demonstrate in the al-Tadamun area in Damascus on Sunday. Editor's note: Image released by the opposition Shaam News Network.

Fighting between opposition and government forces in the Syrian capital Damascus erupted for a second day Monday, activists said, one day after the International Committee for the Red Cross declared the conflict to be a civil war.

The decision by the Geneva-based group to label the situation in Syria as a civil war is significant because it means that international humanitarian law now applies throughout the country and attacks by either side on civilians and detainees could constitute war crimes.

"We are now talking about a non-international armed conflict in the country," ICRC spokesman Hicham Hassan said.

Fierce fighting in capital
Monday’s fighting was reportedly some of the fiercest to hit Damascus since the 17-month-old revolt against President Bashar al-Assad began.

The clashes briefly closed the highway linking the capital with Damascus International Airport to the city's south — an unprecedented development, Mustafa Osso, an activist based in Syria, told The Associated Press. 

"It seems there is a new strategy to bring the fighting into the center of the capital," Osso said, referring to the rebels who fight under the banner of the Free Syrian Army. "The capital used to be safe. This will trouble the regime."

Red Cross: Syria conflict is now a civil war

Amateur video posted online has shown clouds of black smoke billowing above residential buildings where opposition rebels and government forces battled. The authenticity of the video could not be independently confirmed.

The Britain-based Syrian Observatory for Human Rights and Osso said the fighting was concentrated in the districts of Kfar Souseh, Midan and Tadamon.

There have been sporadic clashes in Damascus in recent months, although Assad's forces remain firmly in control of the capital. Many of the Damascus suburbs, however, have risen up against the regime, prompting a ferocious response from the military in an attempt to clear out rebel fighters from the towns that ring the capital.

The spread of fighting in the capital came as U.N. peace envoy Kofi Annan starts a two-day visit to Moscow. He will meet Russian President Vladimir Putin, who has resisted Western calls to increase pressure on Assad.

Russian Foreign Minister Sergei Lavrov signaled no change in its position on the conflict before talks with Annan.

UN investigates Syria massacre site

Lavrov said Western efforts to pass a Security Council resolution to extend the U.N. monitoring mission in Syria, which includes a threat of sanctions, contained "elements of blackmail." He called for support of Moscow's resolution instead, which does not call for sanctions.

The monitoring mission was suspended due to rising violence in Syria, where activists say more than 17,000 people have died.

At least five people were killed and dozens more wounded in Sunday's fighting, according to activists who said they expected more casualties from the violence on Monday.

Accounts in Syria are difficult to verify because the government has restricted access to international media.

Ambassador expelled
Pressure on Assad has been growing both from outside the government and within.

Morocco asked Syria's ambassador to the country to leave and declared him persona non grata. The move comes days after the Syrian ambassador to Iraq defected to the opposition, and a week after top general and Assad insider Manaf Tlas fled Syria.

The Guardian newspaper cited reports Monday that Maj. Gen.  Adnan Sillu, the former head of Syria's chemical weapons program, had defected to the opposition.

Rising violence in Syria, including several alleged massacres in the country, has increased outrage in Syria. What began as peaceful protests has morphed into an armed insurgency fighting back fiercely against Assad's heavy crackdown.

Annan is visiting Moscow just days after opposition reported a new massacre in the village of Tremseh which prompted a fresh wave of denunciations in the West, where diplomats still hope Russia might ease support for Assad.

US source: Syria is moving its chemical weapons

Moscow, along with China, has blocked tougher U.N. Security Council action and the West has shown no appetite for the kind of intervention it undertook last year when NATO helped topple Libya's Moammar Gadhafi.

Annan said Friday he was "shocked and appalled" at the government for breaking a promise not to use heavy weapons in populated areas, and that it was confirmed that helicopters and artillery had fired on the village of Tremseh on Thursday.

U.N. monitors who managed to enter Tremseh have said that the fighting there did not constitute a massacre, as alleged by opposition activists, but that it could more likely be described as a lopsided flight between the Syrian military on the one side and army defectors and residents who tried to defend the town on the other.

The Syrian government said it killed several dozen enemy fighters in Tremseh but denied carrying out a massacre or that its forces used heavy weapons.

Syrian Foreign Ministry spokesman Jihad Makdissi criticized Annan for jumping to conclusions by accepting opposition reports of the incident last week.

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"Government forces did not use planes, or helicopters, or tanks or artillery," he told a news conference in Damascus. "What happened was not a massacre. ... What happened was a military operation."

NBC News' Ayman Mohedin, Reuters and The Associated Press contributed to this report.

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Updated at 2:01 p.m. ET: The International Committee of the Red Cross said on Sunday it now considers the conflict in Syria a civil war, meaning international humanitarian law applies throughout the country. The declaration came as opposition fighters battled Syrian government forces in Damascus.

The Geneva-based group's assessment is an important reference that helps parties in a conflict determine how much and what type of force they can or cannot use.

ICRC spokesman Hicham Hassan said Sunday that the humanitarian law now applies wherever hostilities are taking place in Syria, where fighting has spread beyond the hotspots of Idlib, Homs and Hama.

International humanitarian law grants parties to a conflict the right to use appropriate force to achieve their aims. But attacks on civilians and abuse or killing of detainees can constitute war crimes.

Syria denied U.N. claims that government forces used heavy weapons during a military operation that has brought widespread international condemnation against President Bashar Assad's regime.

Syrian Foreign Ministry spokesman Jihad Makdissi said the violence Thursday was not a massacre, but a military operation targeting armed fighters who had taken control of the village of Tremseh.

"What happened wasn't an attack on civilians," Makdissi told reporters in Damascus. "What has been said about the use of heavy weapons is baseless."

But the United Nations has already implicated Assad's forces in the assault. The head of the U.N. observer mission said Friday that monitors stationed near Tremseh saw the army using heavy weaponry and attack helicopters.

On Saturday, U.N. observers investigating the killings found pools of blood in homes and spent bullets, mortars and artillery shells, adding details to the emerging picture of what anti-regime activists have called one of the deadliest events of Syria's uprising. The observers were expected to return to Tremseh on Sunday.

Dozens of people have already been buried in a mass grave, and activists are still struggling to determine the total number of people killed in what they say was a bombardment by government tanks and helicopters on Thursday.

Some of the emerging details suggested that, rather than the outright shelling of civilians that the opposition has depicted, the violence in Tremseh may have been a lopsided fight between the army pursuing the opposition and activists and locals trying to defend the village. Nearly all of the dead are men, including dozens of armed rebels. The U.N. observers said the assault appeared to target specific homes of army defectors or opposition figures.

Running tolls ranged from around 100 to 152, including dozens of bodies buried in neighboring villages or burned beyond recognition. The activists expected the number to rise since hundreds of residents remain unaccounted for, and locals believe bodies remained in nearby fields or were dumped into the Orontes River.

Independent verification of the events is nearly impossible in Syria, one of the Middle East's strictest police states, which bars most media from working in the country. The observers are in the country as part of an all but mordant peace plan by U.N. special envoy Kofi Annan, who has been trying for months to negotiate a solution to Syria's crisis.

In Damascus on Sunday, numerous residents contacted by Reuters said they could hear loud explosions, persistent gunfire and sirens wailing. Thick black smoke was visible above the Damascus skyline in live internet video links.

"I can't believe it, it sounds incredibly close. I hear shooting and other stuff, like blasts. I can hear the sounds of ambulances rushing past. I am so afraid. People may die tonight," said a resident in a district close to the fighting, contacted by telephone.

Activist Samir al-Shami, who spoke to Reuters by Skype from Damascus, said the fighting was under way in the al-Tadamon district in the capital's south, after a night of sustained battles in the nearby Hajar al-Aswad district.

"There is the sound of heavy gunfire. And there is smoke rising from the area. There are already some wounded and residents are trying to flee the area," he said, using Skype to show live video images of smoke visible over the skyline.

"There are also armored vehicles heading towards the southern part of the neighborhood," he said.

Like others contacted by Reuters, he described it as the most intense fighting he had heard in the capital.

"This area has had a lot of fighting ... The area is kind of a slum. The people who live there are poor. There's a lot of people and a lot of grassy areas around it so it's easy for rebels to sneak in and out," he said.

An explosion hit a security forces bus in Damascus on Sunday and wounded several people, activists said. Residents said they heard a powerful blast, followed by the sirens of ambulances rushing toward Damascus's southern ring road near the neighborhood of Midan.

Meanwhile, the Iranian foreign minister was quoted as saying that Iran is ready to host talks between the Syrian government and opposition groups, but members of the opposition quickly rejected the offer.

The statement by Foreign Minister Ali Akbar Salehi appeared to suggest a possible shift in the Iranian leadership's approach. Iran has consistently supported Assad's efforts to suppress the 17-month-long uprising.

Tehran has repeatedly accused Western and regional powers of meddling in Syria's internal affairs through backing extremist militant groups.

"The Islamic Republic of Iran is ready to sit down with the Syrian opposition and invite them to Iran," Salehi was quoted as saying by the Iranian Students' News Agency. "We are ready to facilitate and provide the conditions for talks between the opposition and the government."

Samir Nashir, an executive board member of the exile Syrian National Council, turned down the offer.

"We will not participate in any meetings or talks with the regime as long as Assad is in power. Assad does not need talks, he needs to go to the International Criminal Court for the massacres he's committed," he said.

"We will not speak to any mediators whether they are Iranian, Syrian or Russian."

The Associated Press, Reuters and msnbc.com's Alastair Jamieson contributed to this report.

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Updated at 630 p.m. ET: United Nations observers found blood, burned homes and signs of artillery fire in the Syrian village of Tremseh on Saturday but were unable to confirm activists' reports that about 220 people were massacred in an attack that prompted international outrage.

The investigation came along with two other key developments in the reported mass slaying by regime forces, who activists say have killed more than 17,000 people since the uprising against killings by President Bashar Assad’s rule began in March 2011:

• Turkey's prime minister blasted Damascus' leadership, warning that the Syrian people will "make them pay" for such mass killings.
• The International Committee of the Red Cross now views fighting in Syria as an internal armed conflict — a civil war in layman's terms — crossing a threshold experts say can help lay the ground for future prosecutions for war crimes.

On Saturday, an 11-vehicle team of observers went into the central village of Tremseh after receiving confirmation a cease-fire was in place, said spokesman for the U.N. mission in Syria Ahmad Fawzi. It was the first outside look into the village where activists say at least 150 people were killed by government troops who shelled the town before moving in alongside pro-regime militiamen.

Anonymous / AP

This image made from amateur video from Hama Revolution 2011 and accessed by AP video, purports to show a funeral for victims killed by violence that, according to anti-regime activists, was carried out by government forces in Tremseh, Syria, on Thursday.

"We have sent a large integrated patrol today to seek verification of the facts," Fawzi said.

Details of the killings remain unclear. The Syrian government says 50 people were killed in Tremseh Thursday when its forces clashed with "armed gangs" terrorizing village residents. The regime refers to its opponents as terrorists and gangsters. On Friday, the United Nations blamed government forces for the Tremseh assault, saying U.N. observers deployed near the village saw government troops using heavy weaponry and attack helicopters against it.

US source: Syria is moving its chemical weapons

"The attack on Tremseh appeared targeted at specific groups and houses, mainly of army defectors and activists," the spokesman for the U.N. observer mission to Syria said later in an emailed statement.

"A wide range of weapons were used, including artillery, mortars and small arms."

Opposition activists say government forces killed about 220 people in the village. U.N. observers said they had found a burned school and fire-damaged houses.

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World leaders have heaped criticism on Assad's regime over the Tremseh incident.

A suicide bomber blew up his car in the closest main town to Tremseh on Saturday, killing three civilians and one security officer, Syria's state news agency said.

SANA said the attacker, who camouflaged the bomb with onions, detonated the explosives in the town of Muhrada.

Warning from Turkey
The prime minister of Turkey — once an ally of Assad before turning against him early on in the uprising over the regime's bloody crackdown, blasted Syria's leadership on Saturday over the Tremseh killings.

"These vicious massacres, these attempts at genocide, these inhuman savageries are nothing but the footsteps of a regime that is on its way out," Recep Tayyip Erdogan said. "Sooner or later, these tyrants with blood on their hands will go and the people of Syria will in the end make them pay."

Red Cross declaration
The Red Cross, guardian of the Geneva Conventions setting down the rules of war, previously classed the violence in Syria as localized civil wars between government forces and armed opposition groups in three flashpoints — Homs, Hama and Idlib. But hostilities have spread to other areas, leading the Swiss-based agency to conclude the fighting meets its threshold for an internal armed conflict and to inform the warring parties of its analysis and their obligations under law.

"There is a non-international armed conflict in Syria. Not every place is affected, but it is not only limited to those three areas, it has spread to several other areas," ICRC spokesman Hicham Hassan told Reuters in response to a query.

"That does not mean that all areas throughout the country are affected by hostilities," he said.

The qualification means that people who order or commit attacks on civilians including murder, torture and rape, or use disproportionate force against civilian areas, can be charged with war crimes in violation of international humanitarian law.

This article includes reporting by Reuters and The Associated Press.

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Arshad Butt / AP

Pakistani security officials stand next to covered body of British Red Cross worker Khalil Rasjed Dale at the site in Quetta, Pakistan on Sunday, April 29, 2012.

The International Committee of the Red Cross condemned the murder of its staff member, Khalil Rasjed Dale, and asked Pakistani media not to broadcast a video of his execution.

"We are devastated," ICRC Director-General Yves Daccord said in a statement. "Khalil was a trusted and very experienced Red Cross staff member who significantly contributed to the humanitarian cause."

Dale's beheaded body was found by the roadside on Sunday in the southwestern Pakistan city of Quetta, police and Red Cross officials said. Dale, 60, who was a British doctor, was abducted by suspected militants on Jan. 5 while on his way home from work.

Red Cross via Reuters

Khalil Rasjed Dale is seen in this undated handout photo. The beheaded body of a kidnapped British doctor working for the International Committee of the Red Cross was found by the roadside on Sunday in the southwestern Pakistan city of Quetta, police and Red Cross officials said.

Police discovered Dale wrapped in plastic near a western bypass road in the capital of southwestern Baluchistan province where Baluch separatist militants are fighting a protracted insurgency for more autonomy.

His name was written on the white plastic bag with black marker.

"A sharp knife was used to sever his head from the body," said Safdar Hussain, the first doctor to examine the body. "He was killed about 12 hours ago."

According to The Guardian, a note left with the body read: "This is the body of Khalil who we have slaughtered for not paying a ransom." The note went on to say a video of the execution would also be released.

The newspaper reported that the Red Cross's policy is not to pay ransoms as part of "a consistent and systematic approach that keeps people safe wherever they are."

"We did everything possible to try to get Khalil out and we are very sad that our efforts failed," ICRC's spokesman Sean Maguire told the BBC.

Dale had worked for the ICRC and the British Red Cross in Somalia, Afghanistan and Iraq before coming to Pakistan. He had been managing a health program for Baluchistan for almost a year when he was abducted, the ICRC statement said.

At least four foreigners are currently being held in Pakistan, The Guardian wrote.

Reuters contributed to this report.

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Arshad Butt / AP

Pakistani security officials stand next to covered body of British Red Cross worker Khalil Rasjed Dale at the site in Quetta, Pakistan on Sunday.

QUETTA, Pakistan —The beheaded body of a kidnapped British doctor working for the International Committee of the Red Cross was found by the roadside on Sunday in the southwestern Pakistan city of Quetta, police and Red Cross officials said.

Khalil Rasjed Dale, 60, was abducted by suspected militants on Jan 5 while on his way home from work.

"The ICRC condemns in the strongest possible terms this barbaric act," ICRC Director-General Yves Daccord said in a statement. "All of us at the ICRC and at the British Red Cross share the grief and outrage of Khalil's family and friends."

British Foreign Secretary William Hague also condemned the killing.

"This was a senseless and cruel act, targeting someone whose role was to help the people of Pakistan, and causing immeasurable pain to those who knew Mr. Dale," Hague said in the statement.

A senior police officer said the Pakistan Taliban had claimed responsibility for the killing, saying a ransom had not been paid.

Police discovered Dale wrapped in plastic near a western bypass road. His name was written on the white plastic bag with black marker.

A sharp knife was used to sever his head from the body," said Safdar Hussain, the first doctor to examine the body. "He was killed about 12 hours ago."

Dale is only the third Westerner killed in such a fashion in Pakistan. The others include Wall Street Journal reporter Daniel Pearl in 2002 and Piotr Stanczak, a Polish geologist, in 2009.

The Pakistan Taliban has been fighting a bloody insurgency against the Pakistani state since its formation in 2007. It is close to al Qaida and it claimed credit for a failed car bomb attempt in New York's Times Square in May 2010.

Quetta is the capital of southwestern Baluchistan, Pakistan's biggest but poorest province, where Baluch separatist militants are fighting a protracted insurgency for more autonomy and control over the area's natural resources.

Pro-Taliban militants are also active in the province, which shares borders with Afghanistan and Iran.

Dale had worked for the ICRC and the British Red Cross in Somalia, Afghanistan and Iraq before coming to Pakistan. He had been managing a health program for Baluchistan for almost a year when he was abducted, the ICRC statement said.

"We are devastated," Daccord said. "Khalil was a trusted and very experienced Red Cross staff member who significantly contributed to the humanitarian cause."

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Armed forces loyal to Syrian President Bashar Assad on Saturday bombarded the Jobar residential neighborhood of Homs, where a standoff continued between a Red Cross convoy and the government that has blocked the delivery of food, medical supplies and blankets to the thousands still stranded in the area.

Thousands of civilians from another area overrun by the army have taken refuge in the neighborhood, an opposition activist organization said.

"In an act of pure revenge, Assad's army has been firing mortar rounds and ... machine guns since this morning at Jobar. We have no immediate reports of casualties because of the difficulty of communications," the Syrian Network for Human Rights said in statement.

Jobar is adjacent to the district of Baba Amr in Homs, from where Free Syrian Army rebels pulled out this week after almost a month of army shelling. Activists reported mass executions by loyalist troops who subsequently entered the area.

The Local Coordination Committees activist network said mortars slammed into Khaldiyeh, Bab Sbaa and Khader districts of the city early Saturday.

Graphic: The siege of Homs

Abu Hassan al-Homsi, a doctor at a makeshift clinic in Khaldiyeh district of Homs, said he treated a dozen wounded.

"This has become routine, the mortars start falling early in the morning," he said. Several homes were damaged from the morning shelling, which he described as steady but intermittent. Most of those he treated were lightly wounded, al-Homsi added.

Aid convoy blocked
The International Committee of the Red Cross (ICRC) said Saturday it was still negotiating with Syrian authorities who have denied its aid convoy access to the shattered Baba Amr district.

An ICRC convoy of seven trucks carrying food and other life-saving relief supplies, joined by Red Crescent ambulances to evacuate the sick and wounded, has been stalled in the city of Homs since arriving there on Friday.

Red Cross convoy prevented from entering former Syrian rebel stronghold

"The ICRC and Syrian Red Crescent are not yet in Baba Amr today (Saturday). We are still in negotiations with authorities in order to enter Baba Amro. It is important that we enter today," ICRC spokesman Hicham Hassan told Reuters in Geneva.

ICRC President Jakob Kellenberger, in a statement issued on Friday after waiting all day for Syrian authorities to grant entry to the team, said the delay was "unacceptable" as civilians had waited for weeks for emergency assistance.

U.N. Secretary-General Ban Ki-moon said on Friday he had received "grisly reports" Syrian government forces were arbitrarily executing, imprisoning and torturing people in the battle-scarred city of Homs after rebel fighters had fled.

PhotoBlog: The fear of carnage to come

'Terrorist' suicide bombs
Meanwhile, the Syrian state news agency Sana reported Saturday that a suicide bomber killed two people and wounded several others in the southern town of Deraa.

"The terrorist explosion led to the martyrdom of two citizens," the agency said.

The British-based Syrian Observatory for Human Rights also reported that at least two people were killed and several others wounded in the explosion.

Syrians flee to northern Lebanon

Syria has seen a string of suicide bombings, the last on Feb. 10, when twin suicide bombs struck security compounds in the government stronghold city of Aleppo, killing 28 people and bringing significant violence for the first time to the city.

The capital Damascus, another stronghold of Assad's, has seen three suicide bombings in the past two months.

The regime has touted the attacks as proof that it is being targeted by "terrorists." The opposition accuses forces loyal to the government of being behind the bombings to tarnish the uprising.

Saturday's bombing in Deraa marked the first time a suicide bombing struck an opposition stronghold. Daraa is the birthplace of the nearly year-old uprising against Assad. The revolt has killed more than 7,500 people, according to most recent U.N. estimates.

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Reuters and The Associated Press contributed to this report.

The Red Cross told Syria on Friday it was unacceptable that its aid convoy had been prevented from entering a battle-scarred district of Homs where the opposition said President Bashar Assad's army had committed a massacre.

Baba Amr became a symbol of resistance to Assad after government troops surrounded it with tanks and artillery and shelled it intensively for weeks, killing and wounding civilians cowering in its ruined buildings.

"It is unacceptable that people who have been in need of emergency assistance for weeks have still not received any help," ICRC President Jakob Kellenberger said in a statement.

"We are staying in Homs tonight in the hope of entering Baba Amr in the very near future."

A convoy of trucks with food and other aid was preparing to enter the shattered district of Baba Amr, the International Committee of the Red Cross, or ICRC, said Friday.

The ICRC received a "green light" from Syrian authorities late Thursday, hours after rebels left the heavily bombarded area following a 26-day siege aimed at crushing a symbol of the revolt against President Assad.

Rebels withdrew on Thursday in a key moment in the year-old uprising against Assad's rule. An official at Syria's Ministry of Foreign Affairs and Expatriates said the army had "cleansed Baba Amr from the foreign-backed armed groups of terrorists."

Activists said Syria's army was hunting down and killing insurgents who had stayed to cover their comrades' retreat, although the reports could not be verified. They said 10 young men were shot dead on Friday.

U.N. Secretary-General Ban Ki-moon made an impassioned plea on Friday for Damascus to grant immediate access for aid workers to besieged Syrian towns, describing the images of death coming out of the country as atrocious.

"The images which we have seen in Syria (are) atrocious," Ban told reporters. "It's totally unacceptable, intolerable. How as a human being can you bear ... this situation? That really troubles me. I'm deeply sad seeing what's happening."

In a rare show of unity with Western powers, Russia and China joined other U.N. Security Council members on Thursday in expressing "deep disappointment" at Syria's failure to allow the U.N. humanitarian aid chief Valerie Amos to visit the country, and urged that she be allowed in immediately.

Russia and China have twice vetoed council resolutions that would have condemned Syria for the crackdown and demanded that it halt the crackdown on anti-Assad demonstrators.

The United Nations says Syrian security forces have killed more than 7,500 civilians during the government crackdown on pro-democracy protesters.

"All violence must stop," said Ban. "I am really urging Syrian authorities to stop (the) violence and allow humanitarian access."

With government forces moving in, the U.N. human rights office voiced dismay over reports suggesting former rebel areas were being subjected to bloody reprisals.

Syrians flee into limbo in northern Lebanon

"We are alarmed at reports starting to come out of the Baba Amr district of Homs after it was taken over by government forces yesterday (Thursday)," U.N. human rights spokesman Rupert Colville told a news briefing in Geneva.

"Although we are not, at this point, in a position to confirm any of those reports, we would like to remind the authorities of their responsibilities under international law.

UN demands immediate 'unhindered' humanitarian access to Syria

"It is essential," Colville added, "that there are no unlawful reprisals, no summary executions, no torture, no arbitrary detention. And the rights of those who are detained must be respected."

Britain's prime minister David Cameron told a press conference in Brussels that "the history of Homs is being written in the blood of its own people" and that the city "is a scene of medieval barbarity."

His concerns were echoed by French president Nicolas Sarkozy, who said France had closed its embassy in Damascus.

Snow delays convoy
ICRC spokesman Hicham Hassan said a joint ICRC and Syrian Arab Red Crescent team, carrying seven truckloads of food and other aid, that left Damascus on Friday morning had faced a weather delay.

"Snow is making the movement of the convoy slower, but we hope to be in Homs within the hour. Red Crescent volunteers and ambulances are waiting in Homs for the convoy to arrive and we are hoping to enter Baba Amr as soon as possible," he said.

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Ayman Mohyeldin, NBC News correspondent in Lebanon, Reuters and msnbc.com staff contributed to this report.