Special envoy Kofi Annan is to visit Damascus on Monday, a day after the United Nations condemned Syria for its use of heavy weaponry in the town of Houla, where at least 108 people have been killed.
Forty-nine children and 34 women were among those who died on Friday, according to the UN. Images of the bodies of children killed by either shelling or shooting have triggered international outrage.
Opposition activists said government forces shelled the town, but President Bashar al-Assad's regime has denied involvement in the killings and says a rebel attack was responsible.
Its ambassador to the UN, Bashar Ja'afari, rejected what he called a "tsunami of lies" from some Security Council members, but did acknowledge there had been a mass killing of civilians in Houla.
The UN Security Council held a three-hour emergency meeting on Sunday. In its statement, it condemned the killings of dozens of men, women and children in attacks that involved a series of government artillery and tank shellings on a residential neighbourhood.
It denounced the killing of civilians by shooting at close range and by severe physical abuse.
General Robert Mood, head of the UN observer mission in Syria, had told the emergency meeting that 108 people were killed and 300 injured in the massacre. He said the deaths were from shrapnel and gunfire at "point-blank" range.
However, the US government said it was horrified by the credible reports of brutal attacks on women and children and called the acts further evidence of an inhuman and illegitimate Syrian government.
Opposition groups said the shelling of Houla by regime forces began at about midday on Friday and continued until dawn on Saturday.
UN observers have visited Houla and confirmed the use of artillery, which only President Assad's forces have, but did not say how all the victims died.
The UN Security Council meeting was called after Russia rejected a French and British proposal for a statement condemning the massacre, diplomats say.
Moscow, which remains a staunch ally of President Assad, told other members of the 15-nation council that it wanted a briefing first from General Mood.
