Davutoglu told reporters on Monday that investigators had obtained "very serious and almost certain" findings linking Kurdistan Workers' Party (PKK) to the bombing on Sunday, the second to hit the Turkish capital in the past month.

So far, no group has claimed responsibility.

DNA tests were ongoing to identify the two possible suicide bombers, the Turkish prime minister added, one of whom was believed to be a woman.

Earlier, police said the woman had joined the PKK in 2013, while the second suspect, a Turkish citizen, also had been linked to the outlawed group.

Arrests and retaliation

Davutoglu said 11 suspects were detained after Sunday's attack, which occurred in central Ankara, close to government ministries and a top courthouse.

In comments broadcast on national TV, he confirmed that Turkey's air force had carried out airstrikes against PKK camps in northern Iraq on Monday.

The death toll from the blast rose to 37 after three people died from their injuries overnight. Davutoglu said forensics teams had, so far, identified 35 bodies.

Around 120 others were wounded when the bomb detonated close to a bus stop, including 15 who remain in intensive care.

Third attack in six months

Sunday's blast comes less than a month after another major car bombing in Ankara, which left 30 people dead and was claimed by a shadowy hardline Kurdish splinter group.

The attacks have raised concerns about Turkey's stability, especially as the country is located so close to war-torn Syria and Iraq.

Twin suicide bombings in Ankara killed 100 people in October and were blamed on the "Islamic State" militant group.

Conflict set to worsen

Violence has spiraled in Turkey's predominantly Kurdish southeast since a two-and-a-half year ceasefire with the PKK collapsed in July.

Kurds have long complained of systemic discrimination in Turkey and are demanding greater autonomy from the state.

The PKK has its bases in the mountains of northern Iraq, from where it controls operations across the frontier in Turkey.

Earlier on Monday, the Turkish air force sent warplanes to carry out air strikes on 18 targets in northern Iraq, including ammunition depots and shelters, the military said.

mm/kms (AFP, AP, dpa, Reuters)