US Secretary of State Hillary Clinton has said that Syrian President Bashar al-Assad has lost legitimacy and is 'not indispensable'.
Her comments come as tension soared over an assault by Assad supporters on the US and French embassies in Damascus.
Mrs Clinton condemned the Syrian attacks and said Washington did not believe the long-time Syrian ruler would follow through on his promises to reform in the face of escalating protests against his rule.
Several Assad loyalists broke into the US embassy in Damascus yesterday and security guards used live ammunition to prevent hundreds from storming the French embassy.
Western diplomats in the Syrian capital said the attackers tore down US embassy plaques and tried to break security glass in protests fuelled by the government against a visit by US and French ambassadors to the city of Hama, the focus of protests against Assad's rule.
A French foreign ministry official said the Syrian authorities had done nothing to stop the assault.
France has led Western attempts to pass a United Nations Security Council resolution condemning Syria's hierarchy for cracking down on protesters.
It says the president has lost legitimacy because of the number of killings to try to quell the protests demanding political freedoms after 41 years of Assad family rule.
The US condemned Syria for 'refusing' to protect the embassy from an assault it said had been encouraged by a pro-government television station, and called in a senior Syrian diplomat to deliver a formal complaint.
Human rights groups say at least 1,400 civilians have been killed since an uprising began in March against Assad's autocratic rule, posing the biggest threat to his leadership since he succeeded his father 11 years ago.