Diyarbakir, Turkey: Turkish warplanes bombed Kurdish militant camps in northern Iraq overnight, hours after a suicide car bomb attack targeting military buses killed 28 soldiers and civilians in the Turkish capital Ankara, security sources said on Thursday.

A car laden with explosives detonated next to the military buses as they waited at traffic lights near Turkey`s armed forces` headquarters, parliament and government buildings in the administrative heart of Ankara late on Wednesday.

The military condemned what it described as a terrorist attack and a senior security source said initial signs indicated that Kurdish militants from the outlawed Kurdistan Workers Party (PKK) were responsible.

The co-leader of the PKK umbrella group, Cemil Bayik, said he did not know who was responsible but the attack could be a response to "massacres in Kurdistan", referring to the Kurdish region covering parts of Turkey, Syria, Iraq and Iran.

The attack, the latest in a series of bombings in the past year mostly blamed on Islamic State, comes as Turkey gets dragged ever deeper into the war in neighbouring Syria and tries to contain some of the fiercest violence in decades in its predominantly Kurdish southeast.

It is part of a US-led coalition fighting Islamic State in neighbouring Syria and Iraq, and has been shelling Kurdish militia fighters in northern Syria in recent days.

It has also been battling PKK militants in its own southeast where a 2-1/2 year ceasefire collapsed last July, plunging the region into its worst violence since the 1990s.

"We don`t know who did this. But it could be an act of retaliation for the massacres in Kurdistan," Bayik was quoted as saying by the Firat news agency, seen as close to the PKK.