Washington and NATO have condemned an attack by a suicide bomber who blew himself up at the US embassy in Ankara killing a Turkish security guard and wounding three other people.

The White House strongly condemned the bombing, saying it was "clearly an act of terror" while saying it did not know yet who was responsible.

However Turkish Prime Minister Recep Tayyip Erdogan said the bomber was a member of the Revolutionary People's Liberation Front (DHKP-C), a radical left-wing group blamed for several attacks since the late 1970s including suicide bombings and attacks on prominent figures.

"It is definitely DHKP-C," Erdogan told the Haber-Turk television network, but he declined to provide further details before DNA test results were available.

The attacker detonated explosives strapped to his body after entering an embassy gatehouse on Thursday.

US officials said the DHKP-C were the main suspects but did not exclude other possibilities.

Turkish media reports identified the bomber as DHKP-C member who had been involved in attacks on a police station
and a military staff college in Istanbul in 1997.

Recent crackdown

Two weeks ago, Turkey carried out a major nationwide crackdown on the DHKP-C group, arresting 85 people.

A court subsequently remanded 38 of them in custody over links to the group which is branded a terrorist organisation by the United States and the European Union.

It most recently claimed a suicide bombing that killed a police officer in Istanbul on September 11.

DHKP-C is vehemently anti-US and anti-NATO, and despises the Turkish establishment. However there was no immediate claim of responsibility for what was the latest of many bloody attacks in Turkey.

In the past officials have blamed Kurdish fighters, leftist extremists or al-Qaeda linked groups.

NATO Secretary General Anders Fogh Rasmussen "strongly condemned" the "outrageous attack on the diplomatic premises of one ally, on the territory of another ally".

The bombing showed "a reckless disregard for human life and for the inviolability of diplomatic staff," he added in a statement.

The embassy warned US citizens to avoid its diplomatic missions in Turkey until further notice and to avoid potential troublespots and demonstrations.

The British mission in Istanbul called on British businesses to tighten security after what it called a "suspected terrorist attack".

In 2008, Turkish gunmen with suspected links to al-Qaeda opened fire on the US consulate in Istanbul, killing three Turkish policemen. The gunmen died in the subsequent firefight.

Source: Agencies