The massive blast struck five buses carrying military service personnel when they stopped at a traffic light in the centre of the capital yesterday evening.
It was the latest in a string of deadly strikes that have rocked Turkey since last summer and one of the deadliest assaults targeting the military in the NATO member state in recent years.
Also today, at least six soldiers were killed in an attack on their convoy in the Diyarbakir region of southeastern Turkey blamed on Kurdish militants, security sources said.
"It has with certainty been revealed that this attack was carried out by members of the terrorist organisation in Turkey in cooperation with a YPG member who infiltrated from Syria," Davutoglu told reporters.
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He said the bomber was a Syrian national named Salih Necar.
Davutoglu warned Russia -- whom Turkey accuses of actively backing the YPG in Syria's civil war -- that Moscow would be "held responsible" if such attacks continued.
Erdogan said 14 people had been detained in nationwide raids over the Ankara bombing.
The attack struck the heart of power in the Turkish capital in an area where the headquarters of the army, the parliament and prime minister's offices are in close proximity.
Pictures showed at least two of the vehicles reduced to burnt-out wrecks, and the massive blast was heard from all over the city, causing panic among locals.
Ankara was already on alert after 103 people were killed on October 10 in a double suicide bombing blamed on the Islamic State (IS) jihadists.
Eighty-one people were wounded, seven of whom are still in intensive care, the health ministry said.
Hours after the attack, Turkey's air force launched new strikes on PKK targets in northern Iraq, acting on intelligence that there were dozens of fighters including top rebel leaders in the area, the army said.