A car bomb killed two people on Thursday outside the main courthouse in Izmir, Turkey's third largest city, as police continue to search for the gunman behind the New Year nightclub attack in Istanbul.

The bomb blast reportedly killed a police officer and a court employee, and wounded five people.

Provincial governor Erol Ayyildiz blamed Kurdistan Workers Party (PKK) militants for the attack.

Two attackers were killed in a shootout with police, while a suspected third attacker is still being sought.