Prime Minister Ahmet Davutoglu said there were "strong indications" that yesterday's attack was carried out by the rebels of the Kurdistan Workers' Party, or PKK.
There was no immediate claim of responsibility for the attack.
Davutoglu added that authorities had detained 11 people directly connected to the suicide bombing near a line of bus stops that killed 37 people.
"There are very serious, almost-certain indications that point to the separatist terror organization," Davutoglu said, referring to the PKK.
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The attack further complicated Turkey's place in the region as it battles a host of enemies across its borders including the Syrian government, Kurdish rebels in both Iraq and Syria, and the Islamic State group, even after being forced to absorb 2.7 million refugees from the conflict.
A fragile, 2 and 1/2-year peace process broke down in July.
Turkey blames the PKK, saying it was inspired by the success of the Kurdish militia forces in Syria against IS in the city of Kobani and elsewhere.
The PKK blames Turkey for failing to deliver on promises.
More than 200 people have died in five suicide bombings in Turkey since July that were blamed either on the Kurdish rebels or IS.
Yesterday's attack was the second suicide bombing in the capital: a February 17 attack for which a PKK offshoot claimed responsibility killed 29 people.
"Ankara's ill-executed Syria policy ... Has exposed Turkey to great risks."
Bill Park, a lecturer on Turkish foreign policy and security at King's College London, said Ankara's aggression toward the Kurds in Syria has angered Kurds inside Turkey and inspired attacks.