WASHINGTON — The Obama administration today closed the U.S. Embassy in Damascus and pulled all American diplomats out of violence-wracked Syria as the U.S. stepped up pressure on President Bashar Assad to leave power.

Robert Ford, the American ambassador, and 17 other U.S. officials left Syria and were expected to travel back to the United States. Ford informed Syrian authorities of the decision to leave earlier in the day, State Department officials said. Two diplomats left by air and the others went over land to Jordan.

Their departure comes two weeks after the State Department warned that it would close the embassy unless Assad’s government better protected the mission, citing safety concerns about embassy personnel and a recent series of car bombs. And it coincides with a U.S. effort to build an international coalition in support of Syria’s opposition.

State Department spokeswoman Victoria Nuland said in a statement that Ford remains the U.S. ambassador “to Syria and its people,” and said he would continue his work on Syria, maintaining contacts with the Syrian opposition and supporting “the peaceful political transition which the Syrian people have so bravely sought.”