A grab taken from the Syrian "Addounia" pro-government television channel shows pro-regime Syrians attacking a US embassy vehicle in Damascus on September 29, 2011. (AFP/Getty Images) (AFP/GETTY IMAGES)

A tomato-hurling mob assaulted the U.S. ambassador to Syria and several aides Thursday as they arrived for a meeting with an opposition leader, an incident the State Department later said was deliberately staged by Syrian officials.

Secretary of State Hillary Rodham Clinton sharply condemned the attack on Ambassador Robert S. Ford, who U.S. officials say was trapped for more than an hour when the mob besieged the Damascus office building where the meeting occurred. No Americans were hurt, but several embassy cars were badly damaged.

“This attempt to intimidate our diplomats through violence is wholly unjustified,” Clinton told reporters at a Washington news conference. A formal complaint was lodged with the government of Syrian President Bashar al-Assad, who Clinton said must “take every possible step to protect our diplomats.”

The White House also denounced the attack, which spokesman Jay Carney termed “an ongoing campaign to intimidate and threaten diplomats attempting to bear witness to the brutality of the Assad regime.”

The outspoken Ford, whose criticism of government repression has repeatedly rankled Syria’s leaders, first came under attack as he arrived in a Damascus office building for a private meeting with an opposition figure, according to a State Department account. News accounts identified the man as Hassan Abdul-Azim, once the head of Syria’s outlawed Arab Socialist Democratic Union Party.

A crowd, described by witnesses as numbering about 100 people, chanted slogans and hurled food at the ambassador as he arrived for the meeting. Afterward, some in the mob battered embassy vehicles while others tried to force their way into the building.

“They tried to break down the door of my office but didn’t succeed,” Abdul-Azim told the Agence France-Presse news agency.

It was the second attack on a Western ambassador in a week, coming days after French Ambassador Eric Chevallier was pelted in similar fashion as he departed a meeting with a Greek Orthodox clergyman in Damascus. That incident also sparked allegations that the Syrian government was inciting mob violence against Western diplomats.

Ford has become a frequent target of criticism by Assad’s government since July, when he made a surprise visit to the restive city of Hama to meet with participants in anti-government demonstrations there. Soon afterward, the U.S. and French embassies came under attack by rock- and vegetable-throwing Assad supporters, some of whom managed to climb over a fence into the U.S. compound before being driven off by guards.