The bomb, which was concealed in a vehicle and went off Monday close to a police station in the city of Gaziantep, near the Syrian border, also injured dozens of people.
The Anadolu agency said anti-terrorism police detained four suspects in the neighboring province of Şanlıurfa on Tuesday. They were taken to Gaziantep for questioning.
No one claimed responsibility for the attack and Kurdish terrorist organization, Kurdistan Workers Party (PKK) insisted they were not involved. Turkey's government, however, has blamed the terrorists.