Western powers expelled Syria's envoys today in outrage at a massacre of 108 people, almost half of them children, and peace envoy Kofi Annan urged president Bashar al-Assad to take bold steps to halt the bloodshed as "a tipping point" had been reached.
The killings in the town of Houla drew a chorus of condemnation from around the world, with the United Nations saying entire families were killed in their homes on Friday, some by army tanks and others probably by pro-Assad militia.
"Bashar al-Assad is the murderer of his people," French foreign minister Laurent Fabius told Le Monde.
"He must relinquish power. The sooner the better."
His Australian counterpart Bob Carr said: "This massacre of more than 100 men, women and children in Houla was a hideous and brutal crime."
UN peacekeeping chief Herve Ladsous, whose monitors are in Syria, contradicted the Assad's government assertion that the killings were carried out by terrorist gangs.
"Part of the victims had been killed by artillery shells, now that points ever so clearly to the responsibility of the government.
Only the government has heavy weapons, has tanks, has howitzers," Mr Ladsous told reporters, adding: "But there are also victims from individual weapons, victims from knife wounds and that of course is less clear but probably points the way to the (pro-Assad) shabbihas, the local militia.
"The United States, France, Britain, Canada, Germany, Italy, Spain, Australia and Bulgaria gave Syria's envoys hours or days to leave their capitals in a coordinated move meant to isolate Assad further diplomatically.
Some had already expelled ambassadors or downgraded ties and so, like Washington, ordered out less senior charges d'affaires.
US state department spokeswoman Victoria Nuland called the Houla attack "the most unambiguous indictment to date" of Damascus's refusal to implement UN resolutions.
"We hold the Syrian government responsible for this slaughter of innocent lives," she said.
Western countries that have called for Dr Assad to step down hope the Houla killings will tip global opinion, notably that of Syria's main protector Russia, towards more effective action against Damascus, perhaps in the form of UN sanctions.
While Western and Arab countries have unilaterally imposed economic sanctions on Syria, Russia and China have blocked any similar move at the United Nations.
French foreign ministry spokesman Bernard Valero said Paris wanted the option of UN sanctions to be looked at seriously, adding: "We are talking to everyone, and especially Russia."
But Moscow, which on Sunday backed a non-binding UN security council text criticising the use of artillery and tanks in Houla, but has twice vetoed tougher resolutions, showed no sign of changing its stance.
Mr Annan, in Damascus to try to save a six-week-old peace plan that has failed to stem Syria's bloodshed, told Dr Assad of the "grave concern of the international community".
"We are at a tipping point," he told a news conference in Damascus.
"The Syrian people do not want the future to be one of bloodshed and division. Yet the killings continue and the abuses are still with us today.
"He urged the armed opposition to cease violence but appealed first to the government, as the stronger party, to take "bold steps now - not tomorrow, now" by stopping all military operations and showing "maximum restraint".
However, Dr Assad's government denied having anything to do with the deaths, or even having heavy weapons in the area, despite the contrary evidence found by United Nations monitors.
Dr Assad himself repeated to Mr Annan Syria's line that "terrorist groups" - Syria's term for the rebels - were stepping up killings and kidnappings across the country.
The estimated number of internally displaced Syrians has more than doubled to 500,000 since an April 12th ceasefire and the flow of refugees abroad has gathered pace again, UN officials said on Tuesday.
UN monitors found spent shells and fresh tank tracks in Houla, evidence of weaponry that Syria's lightly-armed rebels do not have in their arsenal.
But the UN human rights office in Geneva said the bulk of the 108 mostly civilian dead in Houla had been executed at close range. Survivors told UN investigators that the killers were pro-Assad "shabbiha" militiamen, who in the past have assaulted and intimidated hotbeds of opposition to Dr Assad.
"What is very clear is that this was an absolutely abominable event that took place in Houla, and at least a substantial part of it were summary executions of civilians - women and children," said Rupert Colville, spokesman for the UN human rights office in Geneva.
He said 49 children and 32 women were among the victims. "At this point, it looks like entire families were shot in their houses."
The report was at odds with a note sent by Syria to the Security Council that said: "Not a single tank entered the region and the Syrian army was in a state of self-defence ...The terrorist armed groups ... entered with the purpose of killing and the best proof of that is the killing by knives, which is the signature of terrorist groups who massacre according to the Islamist way."
Gruesome video footage distributed by opposition activists has helped to shake world opinion out of growing indifference to a conflict in which more than 10,000 have been killed.
Opposition sources said rebels had killed 20 soldiers in heavy fighting close to the border with Turkey.
They said six civilians and six rebels, including two commanders, had also been killed over the past 24 hours in fighting that began when the army launched an offensive with tanks and helicopters to retake the region around Atareb.
Russian foreign minister Sergei Lavrov told Annan in a telephone call that "all sides" must end the violence, a statement said.
Moscow long saw Dr Assad's late father as the best defender of its interests in the region, and leases a major naval base in Syria. It has suggested that foreign countries are undermining Annan's plan by supporting the opposition.
"We are alarmed that some countries ... are starting to use this event as an excuse to put forth demands of the need for military action in an attempt to put pressure on the UN Security Council," Mr Lavrov told journalists in Moscow.
"We are troubled by the ceaseless attempts to frustrate Kofi Annan's peace plan."
The plan calls for the government to withdraw all heavy weapons from towns and cities, followed by a cessation of fighting and dialogue with the opposition, but has stalled at the first hurdle.
Syrian deputy foreign minister Faisal Mekdad told reporters: "Syria has not committed a single violation of Annan's plan or the initial understanding between Syria and the United Nations.
"At the same time, the other party has not committed to a single point. This means that there is a decision by the armed groups and the opposition not to implement Annan's plan and to make it fail."
Sunni Muslim Gulf powers Saudi Arabia and Qatar favour arming the mostly-Sunni rebels fighting Dr Assad, whose ruling cadre are mostly Alawites - members of an offshoot of Shia Islam.
A military presence is required in Syria to guarantee a potential ceasefire and to protect observers and aid workers, Belgian foreign minister Didier Reynders said today.
"Without asking for intervention like in Libya a real military presence to assure the ceasefire, protect UN observers and protect those who want to do humanitarian work is indispensible," Mr Reynders told reporters.
Reuters