The United Nations said on Saturday that more than 92 people were killed in what activists described as an artillery barrage by government forces on the central Syrian town of Houla.
"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," Major General Robert Mood, the head of the UN team monitoring the ceasefire - which has yet to take hold – said in a statement.
"The observers confirmed from examination of ordinances the use of artillery tank shells," he said, without elaborating, adding, "Whoever started, whoever responded and whoever carried out this deplorable act of violence should be held responsible."
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.
The incident, which represented the worst violence since the start of a UN peace plan meant to put an end to the bloodshed in Syria's 14-month uprising, drew harsh condemnations from the international community.
U.S. Secretary of State Hillary Clinton said in a statement, "Those who perpetrated this atrocity must be identified and held to account. The United States will work with the international community to intensify our pressure on Assad and his cronies, whose rule by murder and fear must come to an end."
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.
U.K. 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 U.N. Security Council - where Russia and China have protected Syria - to "stop the escalation of killing and violence by armed gangs and government military forces."
International envoy and former UN Secretary General Kofi Annan and current UN Secretary General Ban Ki-moon issued a statement condemning the killings. "This appalling and brutal crime involving indiscriminate and disproportionate use of force is a flagrant violation of international law and of the commitments of the Syrian government to cease the use of heavy weapons in population centers and violence in all its forms," they said.
"Those responsible for perpetrating this crime must be held to account," they added, calling on President Bashar Assad to end the use of heavy weaponry in populated areas and end all violence in the country.
Although a 6-week-old ceasefire plan negotiated by Annan has failed to stop the violence, the United Nations is nearing full deployment of a 300-strong unarmed observer force meant to monitor a truce.
The plan calls for a truce, withdrawal of troops from cities and dialogue between the government and opposition.
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