U.S. President Barack Obama has said Syrian President Bashar al-Assad had "lost legitimacy" for failing to lead a democratic transition, but stopped short of calling on him to step down.
Obama's comments to CBS News echoed those by Secretary of State Hillary Clinton a day earlier.
White House spokesman Jay Carney said Assad "is not indispensable" and urged him to lead a transition to democracy.
The heated rhetoric follows an assault by Assad loyalists on the U.S. and French embassies in Damascus on July 11, which has been strongly condemned by the UN Security Council.
State Department spokeswoman Victoria Nuland said the U.S. ambassador to Damascus, Robert Ford, had met with Syria's deputy foreign minister for talks with "a much more collaborative tone."
But Nuland added the United States and its allies would continue to weigh further measures against Syria, including sanctions on its oil and gas sectors and possible referral to the International Criminal Court over the crackdown.
compiled from agency reports