Two security guards were killed in a blast outside the US embassy in Ankara on Friday, local television reported, amid speculation it was a suicide attack.
The force of the explosion damaged nearby buildings in the Cankaya neighbourhood where many other state institutions and embassies are also located.
NTV television reported that a person detonated a bomb at the security roadblock near the entrance to the embassy's visa section, where dozens of people wait every day.
Police have cordoned off the area but there has been no official comment on the blast outside the highly fortified complex.
NTV television said two security guards were killed and several people wounded.
US embassy staff were not immediately reachable for comment.
Predominantly Muslim Turkey is a close US ally and a member of the North Atlantic Treaty Organisation.
The blast comes barely a week after NATO declared that a battery of US-made Patriot missiles went operational on Turkey's border with war-torn Syria on Saturday.
In July 2008, three gunmen and three Turkish policemen were killed in an attack outside the US consulate in Istanbul.
In November 2003, four suicide car-bomb attacks on two Istanbul synagogues, the British consulate and British bank HSBC killed 63 people, including Britain's consul general.
The bombings were claimed by an Al-Qaeda cell.