The US has shut its embassy in Yemen's capital Sanaa, citing "ongoing threats" by an al-Qaeda offshoot linked to an alleged failed US plane bomb plot, BBC reported.
In a statement on its website, the embassy urged US citizens in Yemen to be vigilant and aware of security.
It comes a day after top US soldier Gen David Petraeus visited Yemen to pledge US support for its fight with al-Qaeda.
There is mounting Western concern that Yemen, the Arab world's poorest nation, is becoming an al-Qaeda haven.
"The US Embassy in Sanaa is closed today, January 3, 2010, in response to ongoing threats by al-Qaeda in the Arabian Peninsula to attack American interests in Yemen," said a statement on the embassy website on Sunday.
It is not clear when the mission will reopen.
'Tighten the noose'
On Saturday, President Barack Obama accused al-Qaeda in the Arabian Peninsula of orchestrating a failed Christmas Day attack on a US plane.
The group said last week it had trained 23-year-old Nigerian Umar Farouk Abdulmutallab, who spent time in Yemen last year, to carry out the attempted bombing of the airliner over Detroit.