As U.N. officials cited eyewitness accounts of gunmen slaughtering families in their homes, Western nations expelled Syrian diplomats Tuesday in a coordinated move against President Bashar Assad's regime over the massacre of 108 people.
U.N. special envoy Kofi Annan met with Assad in Damascus to try to salvage what was left of a peace plan, which since being brokered six weeks ago has failed to stop the violence.
Survivors of the Houla massacre blamed pro-regime gunmen for at least some of the carnage.
"It's very hard for me to describe what I saw, the images were incredibly disturbing," a Houla resident who hid in his home during the massacre told the Associated Press on Tuesday.
He said the pro-regime gunmen, known as shabiha, targeted the most vulnerable in the farming villages that make up Houla, a poor area in Homs province. "They went after the women, children and elderly," he said.
U.N. peacekeeping chief Herve Ladsous said there are strong suspicions that pro-Assad fighters were responsible for some of the killings, adding that he has seen no reason to believe that "third elements" -- or outside forces -- were involved, although he did not rule it out.
The Syrian regime has denied any role in the massacre, blaming the killings on "armed terrorists" who attacked army positions in the area and slaughtered innocent civilians.
Following his meeting with Assad, Annan called on the government and "all government-backed militias" to stop military operations and show maximum restraint. He also called on the armed opposition to stop all violence.
"We are at a tipping point," Annan told reporters in Damascus. "The Syrian people do not want the future to be one of bloodshed and division."
Cranking up the pressure on Assad, the Obama administration gave Syria's most senior envoy in Washington, the charge d'affaires at the Syrian Embassy, 72 hours to leave the United States. Britain, Canada, Australia, France, Germany, Italy, Spain and Bulgaria also expelled Syrian diplomats.
"We hold the Syrian government responsible for this slaughter of innocent lives," State Department spokeswoman Victoria Nuland said in Washington. "This massacre is the most unambiguous indictment to date of the Syrian government's flagrant violations of its U.N. Security Council obligations."
White House spokesman Jay Carney said the Obama administration remains opposed to military action in Syria, reasoning that it would lead only to more carnage. He said the U.S. will continue offering non-lethal assistance to the Syrian people.
According to witnesses, the massacre, which began late Friday in an area about 25 miles northwest of the city of Homs, had sectarian overtones.
The victims lived in the Houla area's Sunni Muslim villages. But the shabiha forces allegedly behind many of the killings came from nearby villages populated by Alawites, an offshoot of Shiite Islam.
Most shabiha fighters belong to the Alawite sect, like the Assad family and the ruling elite.