ANKARA,Turkey (AP) — An explosion that hit a police station in the mainly Kurdish city of Diyarbakir was the result of a "terror attack," Interior Minister Suleyman Soylu said Wednesday.

The blast occurred Tuesday at a workshop inside the police complex as an armored police vehicle was being repaired. A police officer and two civilian employees were killed.

Soylu had announced after the explosion that it appeared to be accidental, saying there was no "outside intervention."

On Wednesday, however, he told Haber Turk television in an interview that investigators had concluded that it was an attack by assailants who had dug a tunnel and placed explosives beneath the vehicle repair facility.

"Last night, it became clear that it was a terror attack," Soylu said. "They carried it out with a tunnel dug from outside (of the police station)."

He did not say who was suspected of being behind the attack, which came as Turkey is heading toward a referendum on Sunday on whether to boost the president's powers.

The private DHA news agency said at least five people were detained in connection with the attack.

Rebels of the outlawed Kurdistan Workers' Party, or PKK, who are engaged in a renewed battle against the government forces, have previously targeted police in the region.

The Islamic State group has also carried out deadly attacks in Turkey.