Izmir - Police detained 18 people on Friday in connection with an attack near a courthouse in the western city of Izmir that killed a policeman and a courthouse employee.
Justice Minister Bekir Bozdag said on Friday that Turkish authorities had no doubt that the outlawed Kurdistan Workers' Party, or PKK, "gave the orders" for the attack.
The two assailants were killed in a shootout with police in Thursday's incident in Izmir, Turkey's third-largest city, after they detonated an explosives-laden vehicle at a roadblock. The attackers were armed with automatic rifles, rocket launchers and hand grenades, officials said.
Bozdag spoke before thousands of people at a memorial service for the slain police officer, Fethi Sekin, who authorities say thwarted a larger attack.
He said 18 suspects were rounded up, but did not provide details. There was no immediate responsibility claim.
ISIS claims nightclub attack
The attack was the latest in a string of assaults carried out by Kurdish militants or the Islamic State group that have hit Turkey as it is still grappling with the aftermath of a failed coup in July that has been blamed on a movement led by US-based Muslim cleric, Fethullah Gulen.
It came just days after 39 people were killed in a nightclub in Istanbul during New Year's celebrations. The ISIS group claimed that attack which it said was a reprisal for Turkey's military operations in Syria.
Addressing crowds in the city of Sanliurfa, near the border with Syria, President Recep Tayyip Erdogan reiterated claims that unidentified forces wanting to forestall Turkey's rise were behind such attacks.
"Unfortunately, the hordes of bloodthirsty murderers released on Turkey are continuing their attacks in open co-operation," Erdogan said. "They are feeding them, arming them, strengthening and leading them to unleash them on Turkey."
Erdogan also accused Turkey's allies of aiming to keep his nation out of military operations to drive the ISIS group from Iraq and Syria.
The Turkish leader vowed, however, to press ahead with a military offensive in northern Syria until two key towns have been cleared of IS militants and Syrian Kurdish militia, which Turkey accuses of collaborating with the PKK.
"The arrow has left the bow. We will not stop until al Bab, Manbij and other regions have been purged of terrorist organisations," Erdogan said, in reference to the towns.