A suicide bomber who attacked the US embassy in Ankara, killing himself and a security guard, belonged to an illegal leftist group, according to the Turkish government.

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Turkish interior minister Muammer Guler said the attacker could have been a Turkish national and member of the militant Revolutionary People's Liberation Party-Front (DHKP-C) or another leftist group.

In a statement, the British Consulate in Ankara said: "There has been a suspected terrorist attack on the US embassy.

"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.

Ankara governor Alaaddin Yuksel said the suicide attacker was inside US property when the explosives were detonated.

The blast sent masonry spewing out of the wall of the side entrance, but there did not appear to be any more significant structural damage.

The bomber was also killed.

Turkish guard killed

US Ambassador Francis Ricciardone emerged through the main gate of the building, which is surrounded by high walls, shortly after the explosion to address reporters, flanked by a security detail as a Turkish police helicopter hovered overhead.

"We are very sad of course that we lost one of our Turkish guards at the gate," Ricciardone he said, thanking the Turkish authorities for a prompt response.

A witness saw one wounded person being lifted into an ambulance as police armed with assault rifles cordoned off the area.

"It was a huge explosion. I was sitting in my shop when it happened. I saw what looked like a body part on the ground," said travel agent Kamiyar Barnos whose shop window was shattered around 100 metres away from the blast.

One witness said the blast was audible a mile away.

History of attacks

Islamist radicals, far-left groups, far-right groups and Kurdish separatist militants have all carried out attacks in Turkey in the past.

The main domestic security threat comes from the separatist Kurdistan Workers Party (PKK), deemed a terrorist group by the United States, European Union and Turkey, but the PKK has focused its campaign largely on domestic targets.

Turkey has led calls for international intervention in neighbouring Syria and is hosting hundreds of Nato soldiers from the United States, Germany and the Netherlands who are operating a Patriot missile defence system along its border with Syria, hundreds of kilometres away from the capital.