A car bomb has exploded near a courthouse in the western Turkish city of Izmir, followed by a shootout between three of the assailants and police.
A police officer and a courthouse employee were killed, while the gunfight left two of the assailants dead.
The explosion occurred near a courthouse entrance that is used by judges, prosecutors and other employees.
District mayor Hasan Karadag told NTV television earlier that 10 people were wounded in the explosion and one of them was in serious condition.
A gunfight between three of the suspected attackers and police erupted after the blast, and two of the assailants were killed, he said.
Turkey's state-run news agency said police are looking for a third suspect who was on the run, described as wearing a black coat and a white beret.
Several ambulances and police were dispatched to the scene.
The incident follows a string of attacks, carried out by Islamic State (IS) or by Kurdish militants, which have left Turkey on edge.
Thirty-nine people were killed in a nightclub attack in Istanbul during New Year's celebrations. IS claimed that attack.
On Wednesday, police had detained some 20 people in Izmir believed to have links to the nightclub attacker, who is still at large.
State-run Anadolu Agency said preliminary reports said two police officers were among the wounded who were taken to nearby hospitals.
Turkish police are closing in on the gunman who killed 39 people at an Istanbul nightclub, a senior official said, insisting his possible whereabouts and contacts had been established.
Turkish deputy prime minister Veysi Kaynak said the gunman who attacked Istanbul's upscale Reina nightclub during New Year's celebrations is most probably from China's Muslim Uighur minority and was a "specially trained member of a [terror] cell".
"The security forces have determined his identity, his possible whereabouts have been determined ... His contacts have also been determined," he told the A Haber news channel in an interview.
"We can say that the circle is closing in on him."
Mr Kaynak said authorities believe the man, whose name has not been revealed, is still inside Turkey, although they have not completely ruled out the possibility that he may have escaped.
"Because we have taken utmost measures at our airports, even though we don't rule it out completely, we believe that we will get results from operations inside Turkey," he said.
His comments came hours after police conducted more raids in their hunt for the gunman, detaining several people at a housing complex on the city's outskirts, the state-run news agency reported.
Anadolu Agency said gendarmerie police and special operations teams conducted raids in the Silivri district, detaining an undisclosed number of Uighurs. The report said that those rounded up were suspected of "aiding and abetting" the gunman.
At least 39 other people, including 11 women, are already in custody over suspected links to the attack.
The Islamic State (IS) group has claimed responsibility for the massacre, saying it was in reprisal for Turkish military operations in northern Syria. Most of the victims of the attack were foreigners from the Middle East.
The gunman reportedly escaped in a taxi after the attack.
Turkish media have widely published images of the suspect, including a selfie video filmed at Istanbul's Taksim Square.
Security has been tightened around Istanbul and at border crossings and airports to prevent him from fleeing Turkey.
Deputy prime minister Numan Kurtulmus suggested in an interview with the Hurriyet Daily news newspaper and other sister publications that "foreign intelligence services" could be behind the attack, pointing at the "professional" manner in which it was carried out.
"I am of the opinion that it's not possible for the perpetrator to have carried out such an attack without any support. It seems like a secret service thing. All these things are being assessed," Hurriyet Daily News quoted Mr Kurtulmus as saying in the interview published on Thursday.
A group of about 20 suspects were also detained on Wednesday in a police operation in Izmir, western Turkey.
Anadolu said the suspects are from the largely Muslim Russian republic of Dagestan, as well as members of China's Muslim Uighur minority and from Syria.
They are thought to have lived with the gunman in an alleged IS cell house in the central Turkish city of Konya, the agency reported.
About 20 children who were with the detainees were also taken to a police station.
