Peace envoy Kofi Annan expressed "grave concern" to Syria's President Bashar al-Assad on Tuesday and Western nations threw out its envoys to protest against a massacre of 108 civilians, many of them children, in the town of Houla.
France, Britain, Canada, Germany, Italy, Spain and Australia said they were expelling the Syrian envoys from their capitals in a move that was coordinated with the United States and underlined Assad's diplomatic isolation.
The killings in Houla drew a chorus of powerful condemnation from around the world, with the United Nations saying entire families had been shot dead in their homes.
"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."
Assad's government late on Monday denied having anything to do with the deaths, or even having heavy weapons in the area.
Western countries that have called for Assad to step down were hoping that the Houla killings would tip global opinion, notably that of Syria's main protector Russia, towards more effective action against Damascus.
Annan drew up a peace plan backed by the United Nations and the Arab League to steer a way out of the 14-month-old uprising against Assad. But six weeks after it was agreed by Damascus and the rebels, the bloodshed has barely slowed.
Annan told Assad of the "grave concern of the international community about the violence in Syria, including in particular the recent events in Houla", his spokesman Ahmad Fawzi said in a statement after two hours of talks in Damascus.