The White House condemned a suicide bombing outside the US embassy in Ankara on Friday as a "terrorist attack," but said it did not yet know who was behind it.
White House spokesman Jay Carney said "we strongly condemn" the attack, which killed a Turkish security guard and wounded several other people.
"A suicide bombing on the perimeter of an embassy is by definition an act of terror. It is a terrorist attack," said Carney.
"However, we do not know at this point who is responsible or the motivations behind the attack. The attack itself is clearly an act of terror."
The bombing at a security roadblock near the entrance to the highly-fortified embassy in an upmarket area of the capital was the latest in a series of attacks on American missions in the Muslim world.
Vice President Joe Biden, on a visit to Germany, said the bomber was believed to be a member of an illegal "left wing terrorist organization," without elaborating.