The UN Security Council on strongly condemned the Syrian government for using artillery in a massacre in which at least 108 people were killed and 300 others injured.
UN officials said the slaughter in Houla -- the subject of an emergency Security Council meeting -- claimed the lives of 49 children and 34 women.
Russia, Syria's main ally, signed up to the Security Council statement which "condemned in the strongest possible terms" the killings in the village near the protest city of Homs.
The statement said the deaths had been confirmed by UN observers and were the result of "attacks that involved a series of government artillery and tank shellings on a residential neighborhood."
The 15-nation council made a new demand for President Bashar al-Assad to withdraw heavy weapons from populated areas -- in line with the peace plan of UN-Arab League envoy Kofi Annan -- and said that "those responsible for acts of violence must be held accountable."
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UN Secretary General Ban Ki-moon and Annan have called the Houla massacre a "flagrant violation of international law".
Thousands of people took part in nationwide protests against the Houla killings on Sunday.
The London-based Syrian Observatory for Human Rights reported that a Syrian military offensive on Sunday left 33 people dead in and around the restive town of Hama, bringing the nationwide death toll for the day to 48.
Britain and France had proposed a UN statement making an even stronger condemnation of the Assad government. But Russia would not agree on the wording and demanded a special meeting before approving the statement.
The Syrian government has denied any responsibility for the deaths and Russia still does not accept that the Damascus government is to blame, its diplomats said.
"It still remains unclear what happened and what triggered what," Russia's deputy UN ambassador Igor Pankin told reporters after the meeting.
"There are substantial grounds to believe that the majority of those who were killed were either slashed, cut by knives, or executed at point blank distance," Pankin said before the meeting.
"It is difficult to imagine that the Syrian government would not only shell... but also use point-black execution" against dozens of women and children, he said.
The government was "not at all" to blame for the Houla massacre, Syrian foreign ministry spokesman Jihad al-Makdissi insisted earlier. Syria's UN envoy Bashar Jaafari said accusations of government responsibility were part of a "tsunami of lies" against Damascus.
A UN source told AFP that an investigation had found that an artillery barrage of Houla on Friday was followed by an attack by militia fighters shortly after.
Major General Robert Mood, head of the UN Supervision Mission in Syria (UNSMIS), gave details of the UN investigation by video conference. He said the opposition Free Syrian Army had given a death toll of 116 but that UN observers had seen 108 bodies.
Mood said there were signs of tank shelling, mortar fire and "physical abuse," and said the deaths were from "shrapnel" and gunfire at "point-blank" range, diplomats at the closed-door UN meeting said.
"The evidence is clear, the evidence is not murky, and there is a clear footprint of the government in this massacre," Germany's UN envoy Peter Wittig told reporters.
Special envoy Annan is to go to Damascus on Monday, the Syrian foreign ministry said. He has said he will renew condemnation of the Houla killings as he seeks to rescue his six-point peace plan.
There are now more than 280 unarmed military observers in Syria to monitor a cessation of hostilities that started on April 12 but lurches closer to collapse each day.
UN leader Ban said the Houla massacre has added to pressure on the UN observers, as some in the conflict-stricken country blame them for an increase in violence. He said the observers were now in a "perilous" position.
Annan is to brief the Security Council on Wednesday on his efforts to end the 15-month old crisis. The UN says more than 10,000 people have been killed in the uprising against Assad, while Syrian activists put the figure at over 13,000.
Ban and Annan have led international condemnation of the carnage which they called an "appalling and brutal crime, involving indiscriminate and disproportionate use of force".
Condemnation has also poured in from the United States, Britain, France and Germany, with French Foreign Minister Laurent Fabius saying he was arranging a meeting of the Friends of Syria group that backs the opposition.
Arab League foreign ministers are to hold their own emergency meeting on the crisis.
In Istanbul, exiled opposition head Burhan Ghalioun on Sunday called for a "battle of liberation and dignity" against the regime until the United Nations allows an international military intervention.
The rebel Free Syrian Army warned that unless the international community took concrete action it would no longer be bound by Annan's peace plan.
TEXT OF UN COUNCIL STATEMENT ON SYRIA
Text of statement agreed on Sunday by the UN Security Council on the Houla massacre in Syria:
"The members of the Security Council condemned in the strongest possible terms the killings, confirmed by United Nations observers, of dozens of men, women and children and the wounding of hundreds more in the village of (Houla), near Homs, in attacks that involved a series of government artillery and tank shellings on a residential neighborhood. The members of the Security Council also condemned the killing of civilians by shooting at close range and by severe physical abuse. The members of the Security Council extended their profound sympathies and sincere condolences to the families of the victims, and underscored their grave concern about the situation of civilians in Syria.
"Such outrageous use of force against civilian population constitutes a violation of applicable international law and of the commitments of the Syrian government under United Nations Security Council Resolutions 2042 and 2043 to cease violence in all its forms, including the cessation of use of heavy weapons in population centers. The members of the Security Council reiterated that all violence in all its forms by all parties must cease. Those responsible for acts of violence must be held accountable. The members of the Security Council requested the Secretary-General, with the involvement of UN Supervision Mission in Syria, to continue to investigate these attacks and report the findings to the Security Council.
"The members of the Security Council demanded that the government of Syria immediately cease the use of heavy weapons in population centers and immediately pull back its troops and its heavy weapons from in and around population centers and return them to their barracks.
"The members of the Security Council reaffirmed their strong commitment to the sovereignty, independence, unity and territorial integrity of Syria, and to the purposes and principles of the Charter.
"The members of the Security Council reiterated their full support to the efforts of the Joint Special Envoy for the implementation of his six point plan in its entirety and requested him to convey in the clearest terms to the Syrian parties, and in particular the Syrian Government, the demands of the Security Council."
