The United Nations said on Saturday that more than 92 people were killed in what activists said was an artillery barrage by government forces in the worst violence since the start of a UN peace plan to slow the flow of blood in Syria's uprising.
The bloodied bodies of children, some with their skulls split open, were shown in footage posted to YouTube purporting to show the victims of the shelling in the central town of Houla on Friday. The sound of wailing filled the room.
The carnage underlined just how far Syria is from any negotiated path out of the 14-month-old revolt against President Bashar Assad.
"This morning UN military and civilian observers went to Houla and counted more than 32 children under the age of 10 and over 60 adults killed," the head of UN team monitoring the ceasefire - which has yet to take hold - said.
"The observers confirmed from examination of ordinances the use of artillery tank shells," Major General Robert Mood said in a statement, without elaborating. "Whoever started, whoever responded and whoever carried out this deplorable act of violence should be held responsible."
In a statement, UN Secretary-General Ban Ki-moon demanded "the Government of Syria immediately cease the use of heavy weapons in population centers".
Activists said Assad's forces shelled the town of Houla on Friday evening after security forces killed a protester and following skirmishes between troops and fighters from the Sunni Muslim-led insurgency fighting Syria's rulers, who belong to the minority Alawite sect.
A British-based opposition group, the Syrian Observatory for Human Rights, said Houla residents fled, fearing more shelling. It said one person was killed in the northern town of Saraqeb when troops fired on a protest against the killing.
Syrian state television aired some of the footage disseminated by activists after the killing in Houla, calling the bodies victims of a massacre committed by "terrorist" gangs.
It also showed video of bodies with what looked like gunshot wounds to the head, sprawled on bloodstained mattresses.
Activists distributed footage appearing to show protests in Aleppo, the largest city in the north.
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, a group that brings together Western and Arab countries keen to remove Assad.
UK Foreign Secretary William Hague said he was coordinating a "strong response" to the killings and would call for the Security Council to meet in the coming days.
In a statement, Arab League head Nabil Elaraby called the killing in Houla a "horrific crime", urging the UN Security Council - where Russia and China have protected Syria - to "stop the escalation of killing and violence by armed gangs and government military forces."