The US ambassador to Syria has been pelted with tomatoes and stones by pro-government supporters as he arrived in the capital of Damascus, according to reports.
Two embassy cars were damaged and a crowd of 100 surrounded the embassy, trapping envoy Robert Ford for three hours, witnesses said. Their attempts to storm the building were unsuccessful.
Ford and other US delegates were on their way to visit Hassan Abdelazim, a politician opposing Syrian President Bashar al-Assad.
Abdelazim has refused to talk to Assad unless the military calls an end to the bloodshed that has stained pro-democracy riots over the past six months.
Eggs and stones were thrown at the French Ambassador Eric Chevallier when he visited Damascus five days ago. A similar incident occurred in July when Ford visited central city of Hama with Chevallier.
The US has been accused of provoking attacks against the military through expressing solidarity with the opposition.
A Syrian Foreign Ministry statement said: "Recent statements from American administration officials ... clearly indicate that the United States is involved in encouraging armed groups to practice violence against the Syrian Arab Army"
An estimated 2,700 people have been killed in violent clashes since the military began clamping down on protests, according to UN figures.