American officials say a mob attacked the U.S. embassy in Syria and the residence of the ambassador Monday.
The U.S. will seek compensation for damage caused after the wall of the embassy compound was breached.
Witnesses said protesters smashed windows and raised a Syrian flag on the compound. They also spray painted anti-American graffiti, witnesses said.
U.S. Marine guards had to fire live ammunition at the mob of what was described as about 300 "thugs." No one was injured in the attacks.
The State Department condemned Syrian security forces who were supposed to be on guard, saying they were slow to respond to the attack.
"We consider that the Syrian government has not lived up to its obligations ... to protect diplomatic facilities and it is absolutely outrageous," Department spokeswoman Victoria Nuland said.
The protests were over visits by the U.S. and French ambassadors last week to the opposition stronghold of Hamas in central Syria.