A suicide bomber has killed a Turkish security guard at the US embassy in Ankara.
The blast blew the door off a side entrance and sent smoke and debris flying into the street.
Ankara Governor Alaaddin Yuksel said the attacker blew himself up inside US property.
Interior Minister Muammer Guler said the bomber was a member of a far-left group.
The US State Department said it was working with Turkish police to investigate what it described as "a terrorist blast".
Islamist radicals, far-left groups, far-right groups and Kurdish separatist militants have all carried out attacks in Turkey in the past.
"The suicide bomber was ripped apart and one or two citizens from the special security team passed away," said Turkish Prime Minister Tayyip Erdogan, who was attending a ceremony in Istanbul when the blast happened.
"This event shows that we need to fight together everywhere in the world against these terrorist elements," he said.
Far-left groups in Turkey oppose what they see as US influence over Turkish foreign policy.
Turkey is a key US ally in the Middle East with common interests ranging from energy security to counter-terrorism.
It has also been one of the leading advocates of foreign intervention to end the conflict in neighbouring Syria.
Turkey is hosting hundreds of NATO soldiers from the US, Germany and the Netherlands, who are operating a Patriot missile defence system along Turkey's border with Syria.
The US Patriots are expected to go active in the coming days.