The American Secretary of State, Hillary Clinton, has condemned an attack on US diplomats in Syria in which the ambassador was pelted with stones and tomatoes.
A crowd of pro-government demonstrators attacked the ambassador, Robert Ford, and his colleagues as they arrived at a meeting with a leading Syrian opposition figure.
The US State Department says Mr Ford was not injured but several embassy vehicles were damaged and the ambassador had to lock himself in an office to await help from Syrian security.
Mrs Clinton says the ambassador and his aides were conducting normal business when they were attacked.
She called the attack a wholly unjustified attempt to intimidate those who questioned events in Syria.
She said it reflected an intolerance on the part of the Syrian regime and its supporters.
Washington has lodged a formal protest but the BBC reports there are no plans to withdraw Mr Ford, who has been a vocal critic of the Syrian government's crackdown on dissenters.
For its part, Syria - which has been irked by the ambassador's meetings with opposition figures - accused Washington of inciting violence and meddling in its affairs.