Turkish President Recep Tayyip Erdogan has vowed to bring terrorism "to its knees" after an attack in the capital Ankara that killed at least 36 people.
Mr Erdogan said the suicide car bomb would serve only to strengthen the resolve of Turkey's security forces.
The blast in the key transport hub of Guven Park injured more than 100. At least one suspected bomber also died.
Interior Minister Efkan Ala said an investigation would conclude on Monday and those responsible would be named.
No group has admitted carrying out the attack, but government sources are casting suspicion on the outlawed Kurdistan Workers Party (PKK).
The Kurdish rebels have carried out a series of attacks on Turkish soil in recent months, claiming hundreds of lives, after a ceasefire ended last year. The so-called Islamic State group has also targeted Ankara recently.
Turkey is part of the US-led coalition against IS and allows coalition planes to use its air base at Incirlik for raids on Iraq and Syria.
It has also been carrying out a campaign of bombardment against Syrian Kurdish fighters of the People's Protection Units (YPG), which it regards as a extension of the PKK.
'Certain success'
Mr Erdogan said in a statement that terror groups were targeting civilians because they were losing the battle against Turkish security forces.
Calling for national unity, he said Turkey would use its right to self-defence to prevent future attacks.
"Our people should not worry, the struggle against terrorism will for certain end in success and terrorism will be brought to its knees," he said.
According to Turkey's state-run news agency, Prime Minister Ahmet Davutoglu has postponed a visit to Jordan following the bombing.
The United States condemned the attack. US State Department spokesman John Kirby said: "We reaffirm our strong partnership with our Nato ally Turkey in combating the shared threat of terrorism."
Nato Secretary-General Jens Stoltenberg also condemned the attack, saying there was "no justification for such heinous acts of violence".
Turkey's pro-Kurdish political party issued a statement condemning the attack. The Peoples' Democratic Party (HDP) said it shares "the huge pain felt along with our citizens".
The HDP is frequently accused of being the political wing of the PKK, an accusation it denies, and of not speaking out against PKK violence.
The blast happened at about 18:40 (16:40 GMT) on Sunday and the area was evacuated in case of a second attack.
Turkish Health Minister Mehmet Muezzinoglu told a news conference that 30 people were killed at the scene and seven died later in hospital. At least one of the dead is believed to be an attacker.
Mr Muezzinoglu said more than 100 people were being treated at several hospitals in Ankara, of whom at least 15 are in a critical condition.
Last month, a bomb attack on a military convoy in Ankara killed 28 people and wounded dozens more.
That bombing was claimed by a Kurdish militant group, the Kurdistan Freedom Hawks (TAK). It said on its website that the attack was in retaliation for the policies of President Erdogan.
Turkey, however, blamed a Syrian national who was a member of the YPG.
Last October, more than 100 people were killed in a double-suicide bombing at a Kurdish peace rally in Ankara.
The BBC's Mark Lowen in Istanbul said three attacks in the Turkish capital in less than six months show the multiple threats that Turkey now faces, and there will be serious questions about the government's ability to maintain security.
The country that was the stable corner of the Middle East and the West's crucial ally in a volatile region is now at a dangerous moment, he said.