The gunman who killed 39 people in an Istanbul nightclub on New Year's Day in an attack claimed by the Islamic State group appears to have been well versed in guerrilla warfare and may have trained in Syria, a newspaper report and a security source said on Tuesday.

The attacker, who remains at large, shot dead a police officer and a civilian at the entrance to the exclusive Reina nightclub on Sunday. He 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.

In a statement claiming the attack on Monday, IS said the shooting was revenge for Turkish military involvement in Syria.

"The assailant has experience in combat for sure. ... He could have been fighting in Syria for years," one security source said, saying that he was likely to have been directed in his actions by the group.

The Haberturk newspaper said police investigations had revealed that the gunman had entered Turkey from Syria and went to the central city of Konya in November, traveling with his wife and two children so as not to attract attention.

CNN Turk said he was believed to be of Kyrgyz origin.

Government spokesman Numan Kurtulmus said on Monday that the authorities were close to fully identifying the gunman, after gathering fingerprints and information on his appearance, and had detained eight other people.

A selfie video of the alleged attacker, apparently walking around Istanbul's central Taksim Square, was broadcast by Turkish news channels on Tuesday as police operations to try to track him down continued.

NATO member Turkey is part of the US-led coalition against IS extremists and since August has been conducting military operations in Syria.

IS extremists have been blamed for at least half a dozen attacks on civilian targets in Turkey over last 18 months. But it was the first time it has directly claimed any of them.

Haberturk cited a barman at the club as saying the gunman had thrown explosive devices several times during the shooting spree, apparently in order to disorientate people and give himself time to reload.