A Syrian mob attacked U.S. Ambassador Robert Ford's convoy in Damascus on Thursday.
White House and State Department officials said no one was injured when a violent mob pelted Ford and several colleagues with tomatoes and eggs as they entered the office of a prominent Syrian opposition figure.
However, they said several heavily armored embassy vehicles sent to help extricate them from the situation were badly damaged with broken windows and dents when the same crowd hurled rocks.
The Obama administration blamed the Syrian government for the incident, saying the attack is part of a larger attempt to intimidate U.S. diplomats in the country.
Secretary of State Hillary Rodham Clinton called the assault on a convoy carrying the U.S. ambassador an "ugly" incident for which Syria's government and security services must answer. She demanded that Syrian authorities protect foreign diplomats.
"We condemn this unwarranted attack in the strongest possible terms," Clinton told reporters at the State Department. "This attempt to intimidate our diplomats through violence is wholly unjustified."
"This inexcusable assault is clearly part of an ongoing campaign of intimidation aimed at diplomats who are raising questions about what is going on inside Syria," Clinton said. "It reflects an intolerance on the part of the regime and its supporters."
The White House said Ford, who was not injured in the attack, will not be recalled from Syria.
Ford and his colleagues had left the embassy Thursday to visit opposition leader Hassan Abdul-Azim, who heads the outlawed Arab Socialist Democratic Union party.
The diplomat has angered the Syrian government in the past by visiting key figures of the anti-government uprising.
The White House said Ford willingly puts himself at risk to support the Syrian people.