Syria has blamed a weekend massacre on "armed groups" amid warnings from the international community that the country is on the brink of civil war.
General Kassem Jamaleddine, the head of the official probe into the killings in the central Syrian town of Houla, told a news conference in Damascus that a preliminary investigation showed that those killed had refused "to oppose the government and were at odds with the armed groups."
Last week's massacre in the central Syrian village of Houla, where 108 people were killed -- many of them children and women -- sparked global outrage. Investigations showed most of those who died were summarily executed.
"The massacre of civilians of the sort seen last weekend could plunge Syria into a catastrophic civil war, a civil war from which the country would never recover," UN Secretary-General Ban Ki-Moon told a forum in Istanbul. "I demand the government of Syria act on its commitment under the Annan peace plan."
Syria's Foreign Ministry immediately reacted to Ban's warning, saying it regretted the comment and accusing the UN chief of becoming a "herald of civil war."
Ban's warning was echoed by British Foreign Secretary William Hague, who said at the same forum that the European Union is preparing new sanctions against Damascus.
The Houla massacre prompted Western countries, including the United States, Britain, France, and Australia to expel senior Syrian diplomats in their countries.
U.S. Secretary of State Hillary Clinton in Copenhagen
Meanwhile, U.S. Secretary of State Hillary Clinton warned that Russia's backing of Assad's regime in the UN Security Council could also lead to a civil war.
Speaking to university students in Copenhagen, Clinton said Russian officials have told her "they don't want to see a civil war."
But she said Washington believes Moscow's policy of protecting Damascus from tough international sanctions in the UN Security Council is, in fact, going to "contribute to a civil war."
"[The Russians] are just vociferous in their claim that they are providing a stabilizing influence. I reject that," Clinton said. "I think they are, in effect, propping up the regime at a time when we should be working on a political transition."
Earlier, Syrian rebels threatened to quit altogether a shaky cease-fire, unless Damascus starts implementing the Annan peace plan in earnest.
In a statement, the Turkey-based Free Syrian Army said that the Houla massacre shows there is no more justification "to unilaterally respect the truce because Assad has buried" Annan's six-point peace plan.
The ultimatum gives the Syrian military until noon June 1 to withdraw troops, tanks, and artillery from all civilian areas and implement an immediate cease-fire.
It calls on Assad's government to grant independent media and humanitarian groups access to all regions and to free all detained protesters and political prisoners. It also demands the launch of "serious negotiations" through UN mediators.
With reporting by AP and AFP