"We are working closely with the Turkish national police to make a full assessment of the damage and the casualties, and to begin an investigation," department spokesperson Victoria Nuland said in a statement.
Nuland called the explosion at the embassy compound's check point at 1:13 p.m. Ankara time "a terrorist blast." A suicide bomber killed a Turkish security guard, blowing the door off a side entrance and sending smoke and debris flying into the street.
An attack at the US Embassy in Turkey's capital on Friday that killed two people was a suicide bombing, Turkish Prime Minister Tayyip Erdogan said.
In comments broadcast live by Turkish television, Erdogan called for a global effort to combat "terrorist elements".
An explosion at the US embassy in the Turkish capital Ankara on Friday was a suspected terrorist attack, the British Consulate-General in Istanbul said, urging British businesses to be vigilant.
"There has been a suspected terrorist attack on the US Embassy in Ankara. Due to the nature of this incident we advise you to be extra vigilant and to take appropriate security measures to safeguard your staff and assets," the British mission said in a statement.
A suspected suicide bomber detonated explosives in an attack which killed two people at the US embassy in Ankara on Friday, the provincial governor Alaaddin Yuksel told reporters.
At least two people have been killed and two injured in an apparent suicide bombing near the US embassy in the Turkish capital Ankara Friday, Turkish media reported.
At least one person was killed in an explosion in front of the US embassy in the Turkish capital Ankara on Friday, the state-run Anatolian news agency and other media reported.
An explosion at a side entrance to the US embassy in the Turkish capital Ankarakilled at least one person on Friday in what some Turkish media said may have been an attack by a suicide bomber.
A Reuters witness saw one wounded person being lifted into an ambulance as police cordoned off the area following the explosion, which sent smoke and debris flying into the street.
Television footage showed a door blown out and masonry from the wall around it scattered in front of the entrance, although there did not appear to be any more significant structural damage.
An explosion in front of the US embassy in the Turkish capital Ankara on Friday wounded several people, Turkish media reported.
A Reuters witness reported a loud explosion in the area and the Dogan news agency said ambulances and fire engines went the to the site.
Voice of Russia, Reuters, dpa