The International Red Cross declares the conflict in Syria to be a civil war. NBC's Ayman Mohyeldin reports on the significance of the designation.
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.
The latest massacre began with a military bombardment of the village of Tremsi. After the heavy artillery and shelling, villagers said pro-government militia men swept in to kill at close range. NBC's Richard Engel reports.
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.
Cousins who defected from the army fled to a valley along with more than 100 other men and boys. For the first few hours they appeared to be safe, until Syrian forces found them. NBC's Richard Engel reports.
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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