Turkish authorities on Tuesday (January 3rd) intensified efforts to identify and detain a gunman who killed 39 people at an Istanbul nightclub who reportedly fought in Syria alongside the "Islamic State of Iraq and the Levant" (ISIL), AFP reported.

Police released pictures of the suspect, who went on the rampage at Reina nightclub on New Year's night, spraying some 120 bullets at guests before slipping away into the night.

So far, 16 people are being held over the attack, which ISIL claimed on Monday, including two foreigners detained by Turkish police at Istanbul's main airport. But the killer remains on the run.

Of the 39 killed in the attack, 27 were foreigners, mainly from Arab countries, with coffins repatriated overnight to countries including Lebanon and Saudi Arabia.

Three Lebanese nationals, two Jordanians and three Iraqis were among the dead, as well as several Saudis.

Reports said police have made progress in the investigation after speaking to the taxi driver who drove the attacker to the club and tracing calls he had made on the driver's mobile phone.

Hurriyet daily said the attacker showed signs of being well trained in the use of arms and had fought in Syria for ISIL.

Hurriyet columnist Abdulkadir Selvi said the attacker had been trained in street fighting in residential areas in Syria and used these techniques in the assault, shooting from the hip rather than as a sniper.

Police meanwhile released the first clear images of the attacker, including one taken by security cameras on the night of the attack.