"The United States has suspended operations of our embassy in Damascus as of Feb. 6. Ambassador (Robert) Ford and all American personnel have now departed the country," State Department spokeswoman Victoria Nuland said in a statement.

Nuland said that the decision to close the embassy came because "the regime failed to respond adequately" to U.S. security concerns.

The spokeswoman said Ford remains "the United States ambassador to Syria and its people," and would continue his work in Washington.

According to media reports, 17 American embassy employees, including Ford, left the country on Monday.

The reports, quoting a senior State Department official, said that deteriorating conditions in Syria made it impossible for the embassy to continue to operate.

The State Department last month said it was considering closing the embassy if the security issues were not addressed.

Ford was called back on Oct. 24 due to threats against him but returned on Dec. 6.

The State Department in October ordered family members of embassy staff in Damascus to leave. On Jan. 11, it ordered a further reduction in embassy staffing due to security concerns.

In an interview aired by NBC on Monday, U.S. President Barack Obama reiterated his call for Syrian President Bashar al-Assad to step down, saying "this is not going to be a matter of if, it's going to be a matter of when."

But when asked if there should be some kind of military intervention like there was in Libya, Obama said "Not every situation is going to allow for the kind of military solution we saw with Libya," adding that "it is very possible" to solve the Syrian crisis without outside military intervention.