The Obama administration has closed the US Embassy in Damascus and pulled all American diplomats out of Syria.
Officials say Ambassador Robert Ford and other diplomats left Syria on Monday. It is the most dramatic US move so far after 11 months of a violent crackdown on dissent by President Bashar al-Assad's regime.
The State Department warned last month it would close the embassy unless Assad's government stepped up its protection. It cited concerns about the safety of personnel and recent car bombs.
The U.N. says Assad's crackdown has killed more than 5,400 people since March. The revolt began with mostly peaceful protests, but armed rebels are now increasingly fighting the regime.
The Obama administration has long demanded that Assad step down. Officials insist his regime's demise is inevitable.