Thirty-four people died when a bomb-laden car exploded at a crowded transport hub in the heart of Turkey's capital Ankara, the health minister said.
Mehmet Muezzinoglu said 125 people were being treated at various hospitals in Ankara, of whom 19 were in a critical condition, after Sunday's bombing.
Turkey's Interior Minister Efkan Ala says authorities will release the name of the organisation responsible for the explosion once the investigation finishes on Monday.
"I believe the investigation will be concluded tomorrow and the findings will be announced," Efkan Ala said in comments broadcast live on television.
The blast -- the second such attack in the administrative heart of the city in less than a month -- could be heard several kilometres away.
It sent burning debris showering down over an area a few hundred metres from the Justice and Interior Ministries, a top courthouse, and the former office of the prime minister.
Police helicopters hovered overhead as a large cloud of smoke rose over the city centre.
One senior security official told Reuters initial findings suggested the attack had been carried out by the Kurdistan Workers Party (PKK) or an affiliated militant group, but there was no immediate claim of responsibility.
The government blamed the PKK and Kurdish militants in Syria for the previous car bombing just a few blocks away on February 17, which killed 29 people, most of them soldiers.
President Tayyip Erdogan spoke with Interior Minister Efkan Ala by telephone after Sunday's blast, presidential sources said.
State broadcaster TRT said the car had exploded at a major transport hub, hitting a bus carrying some 20 people near the central Guven Park and Kizilay Square. It said the area was crowded when the explosion happened at 6.43pm local time.
NATO member Turkey faces multiple security threats. As part of a US-led coalition, it is fighting Islamic State in neighbouring Syria and Iraq. It is also battling PKK militants in its southeast, where a 30-month ceasefire collapsed last July, triggering the worst violence since the 1990s.
After locals uploaded images and video of the aftermath, Turkish authorities blocked access to social media sites like Twitter and Facebook.
Last month's attack targeted a military convoy, less than 500m from the country's parliament buildings and only a few blocks away from today's explosion.