The arrests come after the Islamic State (IS) militants claimed responsibility for the carnage. The group said in a statement the attack was carried out by “a heroic soldier”.
“In continuation of the blessed operations that Islamic State is conducting against the protector of the cross, Turkey, a heroic soldier of the Caliphate struck one of the most famous nightclubs where Christians celebrate their apostate holiday,” the statement said.
The IS released the statement on the encrypted messaging service Telegram and accused Turkey of shedding the blood of Muslims through “its airstrikes and mortar attacks” in Syria.
Eight suspects were taken into custody by Istanbul anti-terrorism squads and they were being questioned. The gunman, who escaped after carrying out the attack, wasn’t among the arrested, said the news agency.
Meanwhile, investigators released a fresh image on the attacker. The image from a security camera showed a slim young man wearing a dark jacket apparently standing at a shop counter.
According to Hurriyet daily, initial police reports suggest the gunman may be from Uzbekistan or Kyrgyzstan. Officials were also investigating the possibility that the attacker may even be from Xinjiang in eastern China and aged around 25.
The attacker looks like a professional who received military training on how to use a weapon, said security experts in Turkey.
“The attacker looked determined, faithful, practical, coldblooded, expert and knows how to get results,” anti-terror expert Abdullah Agar said.
“He probably fired these bullets before in real clash zones. He had no hesitation in shooting at innocent people. He is absolutely a killer and he most probably shot at humans before,” Agar added.
The gunman killed a police officer and civilian outside the venue on the European shore of the Bosphorus before entering and opening fire on New Year’s Eve revellers.
Eleven Turks and 28 foreigners died late on Saturday when the gunman entered Istanbul’s popular nightclub Reina, which was packed with around 600 revellers.
The killer randomly fired up to 180 bullets at people with a long-barrelled gun in an assault lasting seven minutes.
Two Indians — Abis Rizvi and Khushi Shah — were among the victims. Rizvi was a film producer and son of former Rajya Sabha member Akhtar Hassan Rizvi whereas Shah was from Gujarat.
Seven of the victims were from Saudi Arabia, three each from Iraq and Lebanon, two each from Jordan, India and Morocco and one each from Syria, Israel, France, Tunisia, Belgium, Kuwait, Canada and Russia.
The body of one victim was not immediately identified. Three people wounded in the assault remain in critical condition, Turkish Prime Minister Binali Yildirim said.
Security measures have been heightened in major Turkish cities since the attack, with the police barring traffic from key squares in Istanbul and in the capital Ankara.