United Nations observers confirmed Saturday, after visiting a town in central Syria, that 92 people had died there - among them 32 children - in what activists said was shelling by government forces, dpa reported.
The head of the UN observers in Syria, Robert Mood, described the incident in the town of Houla as a "brutal tragedy."
Members of the UN team toured Houla to assess the situation after reports of a massacre in the town, where activists said more than 100 people were killed on Friday night after heavy shelling on the area by Syrian troops.
Blasts and gunfire were heard in Houla, 200 kilometres north of Damascus, as the observers arrived in the town, activists said.
The reported massacre was one of the worst in Syria's 15-month uprising.
The rebel opposition Free Syrian Army (FSA) called on the UN to meet its responsibilities and stop the violence in Syria. Otherwise, it said, the group could no longer commit to the ceasefire brokered by UN-Arab League envoy, Kofi Annan.
Annan earlier this year brokered a six-point peace plan, which included a ceasefire that went into effect on April 12. The ceasefire has been breached on several occasions since it was reached.
Video footage posted on YouTube showed the bodies of dead children in Houla with shrapnel wounds on a floor. The sound of wailing could be heard.
State television aired some of the footage posted by activists on their websites, saying the bodies of victims were massacred by "terrorist" gangs.
The government has frequently blamed "armed terrorist groups," backed by Arab and foreign powers, for the violence.
French Foreign Minister Laurent Fabius condemned the violence as a "massacre," and said he wanted to arrange a meeting in Paris of the Friends of Syria, which groups Western and Arab countries working to remove Syrian President Bashar al-Assad from power.
Egyptian Foreign Minister Mohamed Amr described the violence as a "crime that cannot be tolerated" and called for an immediate investigation to determine those responsible for it.
The opposition Syrian National Council, which groups exile opposition figures, urged the UN and the Arab League to convene emergency meetings to discuss the alleged massacre.
In a statement, Arab League head Nabil Al-Arabi called the killing in Houla a "horrific crime" and urged the UN Security Council to "stop the escalation of killing and violence by armed gangs and government military forces."
The Syrian Observatory for Human Rights said many people left Houla after the reported massacre, which sparked protests in the northern city of Aleppo.
The Observatory said one person was killed and 10 wounded in the northern town of Saraqeb, where government forces opened fire on protesters.
The surge in violence came as Annan is due in Syria next week.