Syrian police guard the entrance to the office where U.S. Ambassador Robert Ford was pelted with eggs and tomatoes. (Bassem Tellawi/AP)

As Ford entered a Damascus office Thursday for a meeting with a local opposition figure, Assad supporters pelted the ambassador with eggs and tomatoes, before trying to storm the building by breaking the locks off the doors.

Ford was trapped in the office for three hours until security forces escorted him out.

Ford has been attacked before, including last month when a pro-Assad protester approached Ford from the back and tried to wrap him in a poster featuring Assad’s face. The ambassador’s security managed to rush him safely into a car:

An outspoken critic of Assad’s crackdown, Ford has also angered the Syrian regime by visiting several protest centers outside of Damascus to show solidarity with the anti-government uprising.

Tensions have been rising between the U.S. and Washington in recent months.

In August, President Obama told Assad to resign to because he had lost legitimacy as a ruler. Washington and the European Union have also imposed sanctions on Assad and other officials, citing the deaths of some 2,700 people since the uprising began.

Syria has responded by accusing the U.S. of helping incite violence in Syria.

The attack on Ford came five days after Assad supporters threw eggs and stones at France’s ambassador as he left a meeting in Damascus. Ambassador Eric Chevallier was unharmed.