The White House said that President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan also agreed during a phone call on the need for an "immediate halt of all bloodshed and violence against the Syrian people" by forces loyal to Assad.
"The two leaders underscored the urgency of the situation, reiterated their deep concern about the Syrian government's use of violence against civilians and their belief that the Syrian people's legitimate demands for a transition to democracy should be met," the White House said in a readout of the call.
Meanwhile, Syrian forces killed at least 14 people today, with the army storming two more towns in pursuit of anti-regime protesters, defying Western calls for an end to violence after a "chilling" UN Security Council briefing.
The killings occurred soon after columns of tanks entered the town of Qusayr in the central province of Homs early on Thursday, sending residents fleeing into the fields, rights activist there said.
"The security forces opened fire on residents who tried to flee to the Al-Basateen district, killing at least five" one activist told AFP in Nicosia, adding later that the death toll rose to eleven.