Images of bloodied and lifeless young bodies, lain carefully side by side after the killings in Houla on Friday, triggered shock around the globe and underlined the failure of a six-week-old U.N. ceasefire plan to stop the violence.
Syrian authorities blamed "terrorists" for the massacre, among the worst carnage in the 14-month-old uprising against President Bashar al-Assad, which has cost about 10,000 lives.
"Women, children and old men were shot dead. This is not the hallmark of the heroic Syrian army," Foreign Ministry spokesman Jihad Makdesi told reporters in Damascus.
Opposition activists said Assad's forces shelled the town of Houla after a protest and then skirmishes between troops and fighters from the Sunni Muslim-led insurgency.
Activists say Assad's ‘shabbiha' militia, loyal to an establishment dominated by members of the minority Alawite sect, then hacked dozens of the victims to death, or shot them at close range.
U.N. military and civilian observers counted 32 children under 10 among at least 92 dead on Saturday. More bodies have since been found, activists said. The observers confirmed the use of artillery, which only Assad's forces have, but did not say how all the victims died.
Western countries and Arab states opposed to Assad put the blame squarely on Damascus.
The Gulf Cooperation Council of Sunni-led monarchies accused Assad's soldiers of using excessive force and urged the international community to "assume its responsibilities to halt the daily bloodshed in Syria".
EU foreign policy chief Catherine Ashton spoke of a "heinous act perpetrated by the Syrian regime against its own civilian population" in a statement on Sunday. The head of the European parliament said it could amount to a war crime.
"Rule by murder"
U.S. Secretary of State Hillary Clinton demanded that those who carried out the killings be 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," she said.
France said it would call a meeting of the Friends of Syria, a group of Western and Arab countries keen to see Assad removed.
Britain said it would summon Syria's envoy over the massacre and that it would call for a meeting of the U.N. Security Council in coming days.
The United Arab Emirates requested an urgent meeting of the Arab League, whose head, Nabil Elaraby, urged the U.S. Security Council to stop the killing.
But there was no immediate official word from Russia, which along with China has vetoed Council resolutions calling for tougher action.
Although the ceasefire plan negotiated by former U.N. secretary-general Kofi 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.
Syria calls the revolt a "terrorist" conspiracy run from abroad, a veiled reference to Sunni Muslim Gulf powers that want to see weapons provided to the insurgents.
The United Nations has accused Assad's forces and insurgents alike of grave human rights abuses, including summary executions and torture.