The United States condemned a Hezbollah-backed assault on the Syrian town of Qusayr, as France kept up the pressure for action over what it said was the regime's use of sarin gas. The condemnation came as efforts stalled to organize a peace conference between the government of Assad and the rebels in Geneva.

Washington accused the regime of President Bashar al-Assad of having relied on Hezbollah fighters from Lebanon to win the battle for the strategic town of Qusayr near the Lebanese border, after rebels were ousted following a devastating 17-day assault. A White House statement condemned the Syrian regime's assault on the town, "which has killed untold numbers of civilians and is causing tremendous humanitarian suffering". Hezbollah, an Iranian backed militia based in Lebanon, has been labeled by the United States as a terrorist organization.

France has said it has proof Syria used deadly sarin gas -- a banned nerve agent. Britain said it also had evidence of sarin use, but had passed it on to the UN for independent verification a week ago and would wait for its findings.

The army said the "heroic victory" in the offensive, launched on May 19, served as a warning that it would "crush" the rebels and bring "security and stability to every inch of our land". The capture of Qusayr opens the way for forces loyal to Assad to move on the central city of Homs, much of which the rebels still control.