Eight suspects were detained on Monday over the deadly terror attack in Istanbul nightclub.
An attacker opened fire on party-goers at the Reina nightclub in Istanbul's Ortaköy district.
At least 39 people, including a police officer, died in the assault.
Sixty-nine people were also injured in the incident.
Meanwhile, Daesh terrorist organization has claimed responsibility for the attack that killed dozens of people.
Nationals of Saudi Arabia, Morocco, Lebanon, Libya, Israel, India, a Turkish-Belgian dual citizen and a Franco-Tunisian woman were among those killed in the attack
Security services had been on alert across Europe for new year celebrations following an attack on a Christmas market in Berlin that killed 12 people.
Only days ago, an online message from a pro-Daesh terrorist group called for attacks by "lone wolves" on "celebrations, gatherings and clubs".