A bomb-laden car caused the explosion late Sunday near Kizilay square, Hurriyet Daily News reported.
The toll was expected to increase as at least nine of those injured were in critical conditions, Health Minister Mehmet Muezzinoglu said on Monday.
A suspected bomber, who also died in the blast, was a female member of the outlawed Kurdistan Workers Party (PKK), security sources said.
Turkish security forces have also arrested 18 suspects following the attack, a government official said.
The arrests were made during operations in Eskisehir and Sanliurfa provinces, the official said.
“The suspects were involved in terrorist propaganda and tried to embrace terrorists. They were involved in various actions,” he said.
Documents related to “illegal organisations” were seized during the raids, he added.
President Recep Tayyip Erdogan condemning the attack said that “Turkey has become a target of terror attacks due to the instabilities in the region.”
“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.
While Turkey’s Supreme Court Head Ismail Rustu Cirit has said that the country must learn “to live with terror”.
“Unfortunately, our country has to live with this terror but the perpetrators, those who wish to attain their goals through terror, should know they will never reach their aim,” the head said.
According to sources, Prime Minister Ahmet Davutoglu has postponed a visit to Jordan following the bombing.
So far, no group has claimed responsibility of the attack, but government sources have cast suspicion on the PKK.
A curfew was declared in three towns in south-east Turkey, while warplanes struck PKK camps in Iraqi Kurdistan.
Eleven warplanes carried out air strikes on 18 targets including ammunition dumps and shelters in the Qandil and Gara sectors, the army said.