A convoy carrying the US ambassador to Syria has come under attack by pro-government demonstrators in Damascus.
Robert Ford was visiting an opposition figure when the American embassy vehicles were attacked by about 200 protesters hurling rocks, street signs and tomatoes.
Police later extracted the convoy to safety and no one was hurt.
US Secretary of State Hillary Clinton said: “We condemn this unwarranted attack in the strongest possible terms. This inexcusable assault is clearly part of an ongoing campaign of intimidation aimed at not only American diplomats, but diplomats from other countries, foreign observers, who are raising questions about what’s going on inside Syria.”
The White House earlier said there was a campaign to threaten diplomats attempting to bear witness to “the brutality of the Assad regime”.
Anti-government demonstrations have continued against President Bashar al-Assad, despite a fierce crackdown by his security forces.
Relations between Syria and numerous countries, including the US, have been seriously damaged, leading to sanctions being imposed.