The State Department said it had pulled all non-essential personnel from Yemen, and the Pentagon said the US Air Force had flown staffers out.
Two US military planes carrying as many as 90 Americans from Yemen were en route to Ramstein Air Base in Germany, CNN reported.
"In response to a request from the US State Department, early this morning the US Air Force transported personnel out of Sana'a, Yemen, as part of a reduction in emergency personnel," Pentagon press secretary George Little said.
The US earlier ordered reduction of embassy staff in Yemen issuing a fresh travel warning of a high security threat level due to terrorist activities and civil unrest.
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The alert came hours after a drone attack killed four Al-Qaeda militants in Yemen and two days after the closure of some two dozen embassies in the Middle East and Africa.
"The Department of State ordered a reduction in the number of emergency US Government personnel in Yemen," State Department spokesperson Jen Psaki said in a statement.
US citizens remaining in Yemen despite the travel warning in effect should limit non-essential travel within the country, she said.
Meanwhile, the British government said it flew the embassy staff in Sanaa back to London overnight.
"Due to increased security concerns, all staff in our Yemen embassy have been temporarily withdrawn, and the embassy will remain closed until staff are able to return," the Foreign and Commonwealth Office said in a statement today.