Prime minister Ahmet Davutoglu, exposing a mosaic of domestic political perils, said Islamic State, Kurdish militant factions or far-leftist radicals could have carried out the bombing.
The attack came as external threats mount for NATO member Turkey with increased fighting across its border with Syria and incursions by Russian warplanes on its air space over the last week.
Turkish investigators worked on Sunday to identify the perpetrators and victims of the attack, as the country began three days of national mourning.
Some have suggested militant nationalists opposed to any accommodation with Kurds seeking greater minority rights could also have been responsible.
Mr Davutoglu’s office named 52 of the victims overnight and said autopsies were continuing.
It said 246 wounded people were still being treated, 48 of them in intensive care.
“The necessary work is being conducted to identify those behind the attack and quickly bring them to justice,” the statement said.