Speaking to NTV network aired Friday morning, Soylu said police detained three suspects early Friday in connection with the terror incident.

"They were detained over tunnel digging. All three suspects are perpetrators. One more suspect remains at large," he added.

A 30-meter (98 feet) tunnel had been dug from the basement of an adjacent building and used to plant about one ton of explosives inside the vehicle maintenance facility, according to Diyarbakir's governorship.

Five people had been detained earlier in connection with the incident.

The explosion martyred two civilian staff members and one police official.

The PKK is listed as a terrorist organization by Turkey, the U.S., and the EU. It has waged a terror campaign against Turkey for more than 30 years, during which more than 40,000 people have lost their lives.