Turkey has established the identity of the gunman who killed 39 people at an Istanbul nightclub on New Year's Day, its foreign minister says.
He said further arrests were made on Wednesday but the attacker himself remained at large.
The gunman shot dead a police officer and a civilian at the entrance to the exclusive Reina nightclub on Sunday then opened fire with an automatic rifle inside, reloading his weapon half a dozen times and shooting the wounded as they lay on the ground.
Islamic State has claimed responsibility for the attack, saying it was revenge for Turkish military involvement in Syria.
"The identity of the person carrying out the attack in Ortakoy has been determined," Turkish Foreign Minister Mevlut Cavusoglu said in a televised interview with the state-run Anadolu news agency. He gave no details.
The gunman appeared to have been well versed in guerrilla warfare and might have trained in Syria, Reuters reported, citing a security source and a newspaper report.
The Haberturk newspaper said police investigations revealed the gunman had entered Turkey from Syria and went to the central city of Konya in November, travelling with his wife and two children so as not to attract attention.
Police detained 27 people as part of the attack investigation in the western city of Izmir on Wednesday, including women and children, who had travelled from Konya, the Dogan news agency said. Video footage showed some of them being brought out of an apartment building to waiting vehicles.
Anadolu reported on Tuesday that 14 people had been detained over the attack while NTV reported that two foreign nationals had been detained at Istanbul's main airport.