He accused the PKK of collaborating in the car bombing, and within hours, Turkish warplanes bombed PKK bases in northern Iraq. Turkey's armed forces will continue their recent shelling of YPG positions in northern Syria, he said, promising that those responsible for the Ankara assault will "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 that the YPG and the PKK were behind the bombing and that 14 people have been detained.
The political arm of the YPG denied involvement in the bombing, and a senior member of the PKK said he did not know who was responsible.
The attack was the latest in a series of bombings in the past year blamed mostly on fighters from ISIL.
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 has taken advantage in recent weeks of a major Syrian army offensive around the northern city of Aleppo, backed by Russian airstrikes, to seize ground from Syrian rebels near the border with Turkey.
That has alarmed Turkey, which fears the advances will stoke Kurdish separatist ambitions at home. It has been bombarding YPG positions in an effort to stop it from taking the town of Azaz, the last stronghold of Turkish-backed Syrian rebels north of Aleppo before the Turkish frontier.
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.
Saleh Muslim, a co-leader of the YPG's political wing, denied that the YPG perpetrated the Ankara bombing and said that Turkey was using the attack to justify an escalation in fighting in northern Syria.
"We are completely refuting that … Davutoglu is preparing for something else because they are shelling us, as you know, for the past week," he told Reuters by telephone.
Turkey has said its shelling of YPG positions is a response, within its rules of engagement, to hostile fire coming from across the border into Turkey — which Muslim also denied. "I can assure you not even one bullet is fired by the YPG into Turkey ... They don't consider Turkey an enemy," he said.
The co-leader of the PKK umbrella group, Cemil Bayik, was quoted by the Firat news agency as saying he did not know who was responsible for the Ankara bombing. But the attack, he said, could be an answer to "massacres in Kurdistan," referring to the Kurdish region spanning parts of Turkey, Syria, Iraq and Iran.
Turkey has been battling PKK fighters in its southeast, where a 2-1/2-year cease-fire collapsed in July and pitched the region into its worst bloodshed since the 1990s. Six soldiers were killed and one wounded on Thursday when a remote-controlled handmade bomb hit their vehicle, the military said.
Davutoglu named the car bomber as Salih Necar, born in 1992, from the Hasakah region of northern Syria, and said he was a member of the YPG.
A senior security official said that the alleged bomber entered Turkey from Syria in July 2014, although he may have crossed the border illegally multiple times before that, and that he had contact with the PKK and Syrian intelligence.
Davutoglu accused the Syrian government of a hand in the Ankara bombing and warned Russia, whose airstrikes in northern Syria have helped the YPG advance, against using the group against Turkey.
"I'd like to warn Russia, which is giving air support to the YPG in its advance on Azaz, not to use this terrorist group against the innocent people of Syria and Turkey," he said. "Russia condemned yesterday's attack, but it is not enough. All those who intend to use terrorist organizations as proxies should know that this game of terror will turn around like a boomerang and hit them first."
Russian President Vladimir Putin's spokesman, Dmitry Peskov, told a teleconference with reporters that the Kremlin condemned the bombing "in the strongest possible terms."