Last Updated 2:54 p.m. ET
(CBS/AP) DAMASCUS - The commander of the United Nations Observers Mission in Syria said Friday that his team has verified the fighting yesterday in Tremseh that activists claim has killed more than 200 people, and said observers are ready to send a larger team into the Hama province village once there is a "credible cessation of violence and a local ceasefire."
Speaking to reporters in Damascus on Friday, Gen. Robert Mood verified that Tremseh had been the target of an assault "involving mechanized units, involving indirect fire impact and involving helicopters. This is what we have seen from a distance of 5 to 6 kilometers [about 3-4 miles]."
An opposition source who spoke to CBS News late Thursday put the death toll at Tremseh at 220.
International envoy Kofi Annan said he was "shocked and appalled" by the reports of the attack. He criticized the government for using heavy weaponry in populated areas, a violation of his struggling peace plan meant to end Syria's crisis.
A member of the Local Coordination Committees opposition group told CBS News that Syrian army forces had surrounded Tremseh Thursday morning and pounded the city with shelling and fire from aircraft, followed by ground assaults by government-backed "shabiha" militias. The opposition group said the attack has begun as a search for soldiers who had defected to join the rebel Free Syrian Army.
The LCC source told CBS News that many of the bodies found at a local mosque were those of army defectors who appeared to have been executed.
President Bashar Assad's regime acknowledged violence in the Tremseh area, saying three soldiers and about 50 civilians were killed when Syrian forces clashed with "armed gangs" that were terrorizing village residents.
The killings will likely fuel further debates between world powers that remain sharply divided on what to try next to stop Syria's violence. All previous efforts, including Annan's plan, have failed to quell the bloodshed.
On Friday White House spokesman Josh Earnest told reporters aboard Air Force One that President Assad had lost the legitimacy to lead through repeated "atrocities" against his people.
Saying she was "deeply saddened and outraged" by news of the massacre in Tremseh, U.S. Secretary of State Hillary Clinton said the U.N. Security Council must make clear to the Syrian regime that there will be consequences for failing o comply with the Anna peace plan. ,/P>
"History will judge this Council," Clinton said. "Its members must ask themselves whether continuing to allow the Assad regime to commit unspeakable violence against its own people is the legacy they want to leave."
Russia's foreign ministry said the massacre only furthered the interests of those seeking to increase sectarian violence in the country.
Two activists reached Friday via Skype who said they were in villages near Tremseh gave similar accounts of the previous day's events.
Bassel Darwish said the army surrounded the village early Thursday to prevent people from fleeing and pounded it with artillery and tank shells and missiles from a combat helicopter until early afternoon.
"We saw the events," he said, adding that he was a few miles from the village. "Lots of people tried to get the families out but they weren't able to."
After the shelling, the army entered with pro-government thugs, known as shabiha, who gunned down and stabbed residents in the streets, he said.
Darwish said activists had compiled the names of about 200 dead, but he did not share the list. He said chaos reigned in the area as residents searched for the dead and missing.
Another activist, Abu Ghazi al-Hamwi, said local rebels, often called the Free Syrian Army, tried to fight off the army but couldn't.
"They kept shelling the city and the weapons that the Free Army had were not enough to keep them out," he said. "So they started trying to get out the wounded and the families by clashing in one place to open a way out."
He, too, put the dead at more than 200, but did not provide a list of names. He said many of the dead were killed when a shell collapsed the roof of a mosque where they had sought shelter.
Another video showed a tank in the street while large booms and gunfire are heard in the background. Activist claims and videos could not be independently verified.
The Syrian government gave a very different story of the Tremseh killing, with the state news agency saying that dozens of members of "armed terrorist groups" had raided the village and were randomly firing on residents.
Security forces clashed with the armed men, killing and capturing many of them, the report said. It said three soldiers and some 50 residents were killed.
The agency provided no photos or videos. Assad's regime considers the country's uprising to be the work of terrorists and extremists, not people seeking reform.
One amateur video posted online late Thursday showed the dead bodies of 15 men lined up on a floor. Some are covered in blood and have wounds to their heads and chests. A second video shows a man's body lying on a hospital gurney.
Yet another video showed a young man wailing over the body of an elderly grey-haired man wrapped in a blanket and lying in the street.
"Come on, Dad. For the sake of God, get up," the man sobs. A boom is heard in the background.
Activists say more than 17,000 people have been killed in the uprising, most of them civilians. The government says more than 4,000 members of the security forces have been killed. It does not provide numbers of civilian dead.
In Damascus Friday Gen. Mood also said that while the escalation of violence is currently obstructing the observers' ability to fulfill their mission, his team is engaging with parties in some localities to facilitate talks between parties.
"Encouraging progress has been made by the parties in Deir Ezzor," Mood said, noting a "significant reduction of violence and growing confidence" in the seventh largest city in Syria.