A suicide bomber and a Turkish guard have been killed in an attack in front of the US Embassy in Ankara.
Turkish officials blamed the attack on left-wing terrorists.
Turkey and the US immediately condemned the attack and US officials urged Americans to stay away from all US diplomatic offices throughout Turkey.
A Turkish woman was also seriously wounded and two other guards suffered lighter wounds in the blast in the Turkish capital, Interior Minister Muammar Guler told reporters.
There was no immediate claim of responsibility, but Mr Guler said “preliminary information” obtained by police indicated that the bomber was likely to be connected to a domestic left-wing militant group.
A police official said the bomber is most likely a suspected member of the outlawed Revolutionary People’s Liberation Party-Front, or DHKP-C.
The group has been designated a terrorist organisation by the United States but had been relatively quiet in recent years.
The explosion occurred inside the security checkpoint at the side entrance to the US embassy, which is used by staff. A guard standing outside the checkpoint was killed while the two guards that were wounded “were standing in a more protected area,” Mr Guler said.
Police and ambulances swarmed the area and authorities immediately cordoned it off. Forensic investigators in white outfits and gloves combed the site.
TV footage showed the embassy door blown off its hinges. The blast also shattered the windows of nearby businesses, littering debris on the ground and across the road. The inside of the embassy did not appear to be damaged.
Television footage also showed what appeared to be a US marksman in a helmet and body armour surveying the area from the roof of an embassy building.
The US Embassy building in Ankara is heavily protected and located near several other embassies, including those of Germany and France. The Hurriyet newspaper said staff at the embassy took shelter in “safe room”.
In a statement, the US Embassy thanked Turkey for “its solidarity and outrage over the incident.”
US Ambassador Francis Ricciardone declared that the US and Turkey “will continue to fight terrorism together” and described the compound as secure.
“From today’s event, it is clear that we both suffer from this terrible, terrible problem of today’s world. We are determined after events like this even more to cooperate together until we defeat this problem together,” he said.
British Foreign Secretary William Hague condemned the attack “in the strongest terms” and said Turkey and the US will get the UK’s full support to find those responsible.
The injured woman was 38-year-old Didem Tuncay, a respected television journalist. A hospital official said she was “not in a critical condition.”
Mr Ricciardone visited Tuncay in the hospital and told reporters outside that he had invited her to the US Embassy for tea.
He also paid tribute to the Turkish guard who was killed, calling him a “Turkish hero” who died defending US and Turkish staff.
Turkey has also seen attacks linked to homegrown Islamic militants tied to al-Qaida.
In a 2003 attack on the British consulate in Istanbul, a suspected Islamic militant rammed an explosive-laden pickup truck into the main gate, killing 58 people, including the British consul-general.