Turkish soldiers walk past by a damaged army vehicle in Lice, Diyarbakir, southeastern Turkey, on Thursday. At least six soldiers were killed on Thursday in an attack on a military convoy in southeastern Turkey blamed on Kurdish militants, security sources said. Photo: AFP

Turkish Prime Minister Ahmet Davutoglu blamed a Syrian Kurdish militia fighter working with Kurdish militants inside Turkey for a suicide car bombing that killed 28 people in the capital Ankara, and he vowed retaliation in both Syria and Iraq.

A car laden with explosives detonated next to 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.

Davutoglu said the attack was clear evidence that the YPG, a Syrian Kurdish militia that has been supported by the US in the fight against Islamic State in northern Syria, was a terrorist organization and that Turkey, a NATO member, expected cooperation from its allies in combating the group.

Within hours, Turkish warplanes bombed bases in northern Iraq of the Kurdistan Workers Party (PKK), which has waged a three-decade insurgency against the Turkish state and which Davutoglu accused of collaborating in the car bombing.

Turkey's armed forces would continue their shelling of recent days of YPG positions in northern Syria, Davutoglu said, promising that those responsible would "pay the price."

"Yesterday's attack was directly targeting Turkey and the perpetrator is the YPG and the divisive terrorist organization PKK. All necessary measures will be taken against them," Davutoglu said in a televised speech.

President Tayyip Erdogan also said initial findings suggested the Syrian Kurdish militia and the PKK were behind the bombing and said that 14 people had been detained.

The political arm of the YPG, denied involvement in the bombing, while a senior member of the PKK said he did not know who was responsible. A co-leader of the YPG's political wing said Turkey was using the attack to justify an escalation in fighting in northern Syria.

The attack was the latest in a series of bombings in the past year mostly blamed on Islamic State militants.

Turkey is getting dragged ever deeper into the war in neighboring Syria and is trying to contain some of the fiercest violence in decades in its predominantly Kurdish southeast.

The YPG militia, regarded by Ankara as a hostile insurgent force deeply linked to the PKK, has taken advantage in recent weeks of a major Syrian army offensive around the city of Aleppo, backed by Russian air strikes, to seize ground from Syrian rebels near the Turkish border.

That has alarmed Turkey, which fears the advances will stoke Kurdish separatist ambitions at home.

Hundreds of Syrian rebels with weapons and vehicles have re-entered Syria from Turkey over the last week to reinforce insurgents fending off the Kurdish-led assault on Azaz, rebel sources said on Thursday.