The US Embassy is the second biggest embassy in Damascus (only the Russian is bigger).
It is one of the most highly protected buildings in the capital (probably only the Presidential Palace has more guards outside it). The Syrian authorities are extemely worried about attacks on the US Embassy.
Some Syrians broke into the building during the 1991 Gulf War (which Syria sent troops to support America) and set fire to the US flag. That was a major embarrasment for the Syrian Government.
One the first day of the Iraq War in 2003, Syrian Riot Police formed a shoulder-to-shoulder blockade of the area up to the Embassy.