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.

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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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NOWSHERA, Pakistan -- There has been little change to the scenes at Jalozai refugee camp in recent years.

Lines of worn and weary wait to register for services, clutching the few belongings they brought with them. Food rations and hygiene packs are distributed inside large tents and makeshift shelters bearing the brands of various United Nations and non-governmental agencies. And children -- some barely toddlers -- are everywhere you turn: packed into temporary tent schools, running through the labyrinthian "streets" of shelters, and holding their parents' places in various lines.

But the thousands that crowd the camp and the area around it today are different from the masses relocated during Pakistan's military operations of 2008 and 2009 in the country's northwest. They are different than the throngs seeking shelter after the devastating floods of 2010 and 2011. The vast majority of the 300,000 the camp currently supports are all from Khyber Tribal Agency bordering Afghanistan, where ongoing fighting between Pakistan's military and militant groups forced them to flee their homes and seek safety elsewhere.

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Tribesmen: US missiles strike village mosque

Unlike the previous groups of arrivals, this new group wasn't anticipated in such large numbers. At the height of the influx in mid-March, the camp was registering 5,000 new families a day. That number has slowed to 400 or 500 a day, but the arrivals continue. Resources the agencies thought would last for months, are now running out.

"Of course, everybody planned for an emergency," says Faiz Muhammed, chief coordinator of Jalozai camp. "But it was planned for, say 10,000 families, maybe for the rest of the year. We're now using up all those resources that were planned for nine months in just two months."

Aine Fay, chairperson of the Pakistan Humanitarian Forum (PHF)-- an informal network of 47 NGOs operating in Pakistan, says the funding situation is dire: less than 3 percent of the required budget to respond to the needs of internally displaced people is available.

"Agencies will run out of money by the end of June if the donor community don't respond," says Fay. "And we're facing into the monsoons of 2012. While we all hope that there will not be a repeat of the floods of 2011 or 2010, we have no guarantee and we have to be prepared for them."

'We're worried'
Robin Lodge, of the World Food Programme (WFP) -- the sole food provider for the Jalozai families -- says the agency has already had to cut back rations to deal with the funding shortage.

"Funding is not too good," says Lodge. "We're worried about the monsoon season because that will put an additional strain on resources."

As the need for their services grows, aid and relief workers are also having to contend with increased insecurity across the country, as they more frequently become targets for kidnapping -- a common means of fundraising for many militant and criminal groups.

Since 2009, according to numbers compiled by PHF, at least 23 aid and development workers -- foreign and Pakistani staff -- have been kidnapped. Eighteen have been killed.

In 2009, eight staff members of two humanitarian organizations in the northwest Khyber-Pakhtunkwa (KPK) province were shot dead in two separate targeted attacks on their office. In 2010, six staff members of one agency were killed in an attack in KPK, and four other staff members were abducted and one was murdered in Balochistan. In 2011, 14 staff from two different organizations were abducted in separate incidents in Balochistan.

So far this year, five humanitarian workers have been abducted and four have been murdered in Balochistan, Sindh and Punjab provinces.

Recently released video of American Warren Weinstein -- kidnapped from his Lahore home in August 2010 -- made headlines as the first sign of life since he was taken. The brutal April murder of Dr. Khalil Dale, a British aid worker with the International Committee of the Red Cross (ICRC) in Balochistan, again brought to the forefront the growing insecurity faced by relief workers in Pakistan.

In response, the ICRC suspended its projects across much of the country as it reassesses its operations, placing local staffers on paid leave and bringing foreign staffers back from the field into Islamabad. This is the first time the agency has suspended operations in Pakistan since it began working here in 1947.

Local, national staff in particular are targeted here -- more visible and more frequently spending time on projects in their own communities than their foreign colleagues who visit sites from time to time. A fake vaccination program carried out by the CIA using local staff in the lead-up to the Osama bin Laden raid created additional problems for local humanitarian workers, leading to suspicion among communities as to aid organizations' true intentions.

Pakistan jails doctor who helped CIA find bin Laden

In February, InterAction -- the largest alliance of U.S.-based international NGOs -- sent a letter to CIA director David Petraeus expressing concern that activities like the vaccination program undermined humanitarian efforts in Pakistan and jeopardized the lives of their staff.

"The CIA's use of the cover of humanitarian activity casts doubt on the intentions and integrity of all humanitarian actors in Pakistan," wrote Samuel Worthington, InterAction's president. "It is imperative that independent, impartial humanitarian action be kept clearly distinct from intelligence-gathering activities. Any blurring of the two risks causing setbacks in decades-long global health and humanitarian efforts and endangers the lives of those working to make advances on the behalf of the global community."

Aid workers from multiple organizations told NBC News that security has always been a part of their planning in Pakistan, but re-assessments and operational re-adjustments have been necessary in recent years as the kidnappings and violence have increased.

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"I think for a lot of organizations, we would measure the vulnerability that communities are at -- the need for the services that we can provide -- versus the risk we think our staff are exposed to," says Fay. "If the risk is greater than the need on the ground, the answer is simple."

Humanitarian workers in Pakistan with whom we spoke, most who wished to remain anonymous, all maintain that despite the risk and the resources they must now divert from aid delivery to security considerations, their priorities remain the same.

"We have had to look at things more carefully, scale up in certain areas of security, re-evaluate," says Stacey Winston, with the UN's office for Coordination of Humanitarian Affairs. "We try to keep security a priority and also to maintain operations as much as possible, because that is really the priority -- to reach as many people as quickly as possible in the humanitarian response."

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AMMAN, Jordan - Syrian Deputy Oil Minister Abdo Hussameldin apparently announced his defection on YouTube, becoming the first high-ranking civilian official to abandon President Bashar Assad since the uprising against his rule erupted a year ago.

"I Abdo Hussameldin, deputy oil and mineral wealth minister in Syria, announce my defection from the regime, resignation from my position and withdrawal from the Baath Party," Hussameldin said in the video, the authenticity of which could not be immediately confirmed.

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"I join the revolution of this dignified people," he said in the video uploaded on Wednesday.

Hussameldin said he had been in government for 33 years but did not want to end his career "serving the crimes of this regime," adding: "I have preferred to do what is right although I know that this regime will burn my house and persecute my family."

Syria strikes not in offing, Pentagon tells Congress

Syrian security forces have killed more than 7,500 civilians during the crackdown on pro-democracy protests, according to the United Nations, and the outside world has proved powerless to halt the killing.

While saying very preliminary military planning was under way, U.S. Defense Secretary Leon Panetta on Wednesday defended U.S. caution in trying to end the violence, despite criticism from legislators who questioned how many people would have to die before the Obama administration used force.

NYT: Under cover of the night, Syrians cross into safety

U.N. humanitarian chief Valerie Amos saw a scene of devastation on Wednesday when she visited the Baba Amr district of the city of Homs that was shelled by the military for nearly a month after becoming a rebel holdout.

'A whole year of sorrow'
Hussameldin said: "I say to this regime: you have inflicted on those who you claim are your people a whole year of sorrow and sadness, denying them basic life and humanity and driving Syria to the edge of the abyss."

Assad appointed Hussameldin, 58, to his current position through a presidential decree in 2009. He said the country's economy was "near collapse". There was no mention of the defection on Syrian state media.

Wearing a suit and tie, Hussameldin looked relaxed as he looked directly into the camera in a tight head and shoulders shot, appearing to read from a prepared statement on his lap as he sat on a dark grey chair against a yellow background.

Opposition sources say the government, controlled by Assad's minority Alawite sect that has dominated power in Syria for the past five decades, has effectively stopped functioning in provinces that have been at the forefront of the uprising, such as Homs and the northwest province of Idlib.

Report: Syrian military hospitals torturing patients

But public defections have remained rare among the civilian branches of the state, despite thousands of the mostly Sunni soldiers and conscripts who make the bulk of the army deserting since the uprising broke out last March.

Amos is hoping to secure access for humanitarian organizations, which have been barred from the zones of heaviest conflict.

Syria had initially failed to grant Amos access to the country but relented after Damascus's allies Russia and China joined the rest of the U.N. Security Council in a rare rebuke of Syria for not allowing her in.

"It was like a closed-down city and there were very few people around," Amanda Pitt, a spokeswoman for the U.N. Office for the Coordination of Humanitarian Affairs said of Amos's visit to Baba Amr on Wednesday, adding it "looked like it was devastated from the fighting and shelling."

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Amos went in with a team of Syrian Arab Red Crescent aid workers, who entered Baba Amr for the first time in 10 days, before heading back to Damascus where she held talks with Syrian Foreign Minister Walid al-Moualem earlier in the day.

He told her Syria was trying to meet the needs of all citizens despite the burdens imposed by "unfair" Western and Arab sanctions, the state news agency SANA said.

Assad's government says the uprising is a campaign by foreign-backed Islamist insurgents that has killed 2,000 police and soldiers since the protests erupted.

Pressure has been mounting on the United States to take some sort of military action, NBC’s Andrea Mitchell reported, but the Obama administration does not want to interene alone. The Arab League and NATO would not back U.S. military action.

President Barack Obama said on Tuesday it was only a matter of time before Assad left office, but has shown no enthusiasm for U.S. participation in an election-year military mission to force him out.

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Panetta told the Senate Armed Services Committee the administration was still trying to forge a consensus on addressing the violence. "That makes the most sense. What doesn't make sense is to take unilateral action at this point."

He and General Martin Dempsey, chairman of the Joint Chiefs of Staff, told the panel that, at Obama's request, the Pentagon had studied U.S. military options in Syria, assessing issues such as potential missions and Syria's troop line-up.

Meanwhile, China's envoy to Syria told Assad's government to stop the violence and help the United Nations and the International Committee of the Red Cross send aid to strife-hit areas, the Chinese Foreign Ministry said on Thursday.

Ministry spokesman Liu Weimin said the envoy also promoted mediation between the Syrian government and opposition groups.

Reuters, NBC News and msnbc.com staff contributed to this report.

Up to 2,000 refugees fleeing violence in Syria are crossing the border into northern Lebanon, a spokesman for the United Nations refugee agency told Reuters on Sunday.

"Between one and two thousand (Syrians) are in the process of coming from Syria to Lebanon," the UNHCR's deputy representative in Lebanon Jean Paul Cavalieri told Reuters.

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"Numbers will become clear in the coming hours. This is what we are hearing from our teams on the ground and local authorities."

A Reuters witness on the Lebanese border heard heavy shelling coming from the nearby Syrian town of Qusair earlier on Sunday and saw mainly women and children fleeing towards Lebanon on foot.

Meanwhile, International Committee of the Red Cross spokesman Sean Maguire told NBC News the organisation was delivering aid around the Baba Amr district of Homs on Sunday, following days of delays, but not in the former rebel stronghold itself.

He said: "Negotiations to enter Baba Amr are ongoing and we still hope to enter that area today. This morning ICRC and Syrian Arab Red Crescent started distributing assistance in a village called Abel, less than two miles from Homs city. The plan is to continue to the neighborhoods of Al Insha'at and Al Tawzii in Homs to populations and to families displaced from Baba Amr."

Earlier, the ICRC said it had been prevented from entering Baba Amr by Syrian ground forces despite receiving government permission, a move activists said was to prevent aid workers witnessing army "massacres".

"We have the green light, we hope to enter, we hope today is the day," said the ICRC's Damascus-based spokesman Saleh Dabbakeh, declining to give further details about what he said were sensitive talks with Syrian officials.

"We are very concerned about the people in Baba Amr."

After a month of bombardment by President Bashar al-Assad's forces, concerns mounted for freezing, hungry and wounded civilians in Homs, which on Saturday had come under renewed shelling by government troops, anti-Assad activists said.

U.N. Secretary-General Ban Ki-moon said on Friday he had received "grisly reports" troops were executing and torturing people in Homs after insurgents abandoned their positions.

South of Homs, the border town of Qusair came under shelling by government troops, forcing residents to flee on foot to neighbouring Lebanon, a Reuters witness said.

"The people said they were sat at home and suddenly the shelling started and they fled. They said it was tank shelling and gunfire," said Reuters reporter Afif Diab.

He spoke at the border to what he said were mainly women fleeing with their children. Blasts could be heard from the Lebanese border, which is some 7 miles from Qusair.

Other Lebanese border sources spoke of attacks in Syria by aircraft, but reports could not immediately be verified.

"Between 1,000 and 2,000 (Syrians) are in the process of coming from Syria to Lebanon," the UNHCR's deputy representative in Lebanon, Jean-Paul Cavalieri, told Reuters.

The United Nations says Syrian security forces have killed more than 7,500 civilians since the revolt against the Assad family's four-decade rule began in March last year.

The Syrian government said in December that "armed terrorists" had killed more than 2,000 soldiers and police during the unrest.

Lebanon deployed more troops to its northern border in response to the violence in Syrian towns nearby, a Reuters witness said, part of a conflict that risks dragging in regional powers with rival sectarian interests.

In the Lebanese capital Beirut, hundreds of soldiers and scores of military trucks and jeeps blocked off the city centre on Sunday during protests for and against Assad, whose ruling clan are Alawites, an offshoot of Shi'ite Islam.

Lebanon is mainly made up of Shi'ites, Sunnis and Christians, and is home to the powerful Shi'ite militant group Hezbollah, which is backed by Shi'ite Iran.

Sunni Arab states Qatar and Saudi Arabia have been among the loudest calling for Assad's downfall, and have even suggested arming his opponents.

"We sacrifice our blood and souls for you Bashar," chanted a pro-Assad crowd of some 500 people. Some stepped on photos of Saudi Arabia's King Abdullah and threw shoes at a poster of him.

A similar sized anti-Assad crowd sang: "We sacrifice our blood and souls for you, Homs."

Former Syrian ally Turkey said Assad was guilty of "war crimes" while China said it was "deeply worrying that the situation in Syria remains grave".

NBC News Correspondent Ayman Mohyeldin, Reuters and msnbc.com staff contributed to this report.

HOMS, Syria – Faced with a daily rain of rockets, bombs and bullets, the people of Homs keep fighting, refusing to yield to President Bashar Assad's forces in an uprising that began 11 months ago.

Their streets and homes have been shelled. They have few medical supplies, no power and very little food. And casualties are mounting. On Wednesday, Syrian forces killed more than 80 people, according to activists, whose claim could not be independently confirmed. But among the dead were two Western journalists.

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There seems to be no way out for the people in this besieged city, reduced to rubble and ruin, yet families and fighters share a moment to dancing in the streets for their “revolution of dignity and freedom.”

A French photojournalist known as Mani, whose full name is being withheld for his own safety, has spent time living alongside the people of Homs. Jonathan Miller, Channel Four Europe reports.

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Updated 10 p.m. ET: GENEVA -- The International Committee of the Red Cross says it is negotiating with Syrian authorities and opposition fighters to broker a cease-fire in some of the most violence-torn areas.

Meantime, activists say Syrian forces opened fire with live ammunition on demonstrators in Damascus overnight, wounding at least four, Reuters reported.

"We are currently discussing several possibilities with all those concerned, and it includes a cessation of fighting in the most affected areas," Red Cross spokeswoman Carla Haddad told The Associated Press.

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She said the talks weren't aimed at resolving entrenched political differences, but to allow the humanitarian agency enough time to deliver aid to civilians hardest hit by the conflict.

"The idea is to be able to facilitate swift access to people in need," Haddad said.

Activists in embattled cities such as Homs say food is running out and doctors lack medicine to treat the wounded.

Violence in capital
Demonstrations and clashes with security forces have hit Damascus in the past week, undermining President Bashar al-Assad's argument that an 11-month uprising has been the work of saboteurs and limited mainly to the provinces.

International diplomacy showed no sign of finding a solution, as Western powers and the Arab League prepared a meeting of "Friends of Syria" Friday to pressure Assad to step down, while Russia and China backed Assad's reform plans, derided by Syria's opposition.

"There were hundreds of demonstrators at the main square of Hajar al-Aswad (neighborhood), and suddenly buses of security police and shabbiha (pro-Assad militia) turned up and started firing into the crowd," activist Abu Abdallah told Reuters by telephone.

He said the four wounded were taken to be treated in homes.

Footage posted on YouTube, purportedly taken before the shooting, showed a crowd marching in Hajar al-Aswad carrying placards in support of the besieged city of Homs and singing "Eyes are shedding tears for the martyrs among Syria's youth."

Earlier, opposition youths unfurled a pre-Assad era national flag over a road bridge at the edge of the capital, YouTube footage showed. That followed a weekend that saw one of the biggest demonstrations yet in the capital as the uprising neared its first anniversary.

‘Cut off from the outside world’
Opposition activists said five people had been killed in government shelling of Homs's Baba Amro district on Monday, adding to a reported death toll of several hundred since the operation began there on February 3.

Activists in the western city of Hama said troops, police and militias had set up dozens of roadblocks, cutting neighborhoods off from each other.

A flood of military reinforcements has been a prelude to previous offensives by Assad's regime, which has tried to use its overwhelming firepower to crush an opposition that has been bolstered by defecting soldiers and hardened by 11 months of street battles.

"Hama is cut off from the outside world. There are no landlines, no mobile phone network and no Internet. House-to-house arrests take place daily and sometimes repeatedly in the same neighborhoods," an opposition statement said.

Rebel fighters have been attacking shabbiha militiamen while avoiding open confrontations with the armored forces that had massed around Hama, a city north of Homs on the Damascus-Aleppo highway.

The government restricts foreign media access in Syria, making it hard to verify the activists' reports independently.

Security forces have killed more than 5,000 people, according to human rights groups, in a campaign to crush the revolt while the Assad government says more than 2,000 soldiers and security agents have been killed.

The Associated Press and Reuters contributed to this report.

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