Gunman identified in Istanbul nightclub attack, authorities say

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ISTANBUL -- The gunman who killed 39 people in the New Year's nightclub terror attack in Istanbul has been identified by Turkish authorities.

Turkish Foreign Minister Mevlut Çavusoglu announced the development Wednesday but did not name the suspect or provide the suspect's nationality.

Authorities have also detained five alleged ISIS members in connection with the attack, state-run agency Anadolu reported Wednesday.

At least 21 people are being held in connection with the attack, though the gunman who carried out the attack at the Reina nightclub in Istanbul still at large.

According to Anadolu, the five were picked up in the Aegean province of Izmir.

ISIS claimed responsibility for the attack in a statement posted to Twitter, but the claim cannot be independently verified by CNN. It boasted about the first major terrorist attack of 2017.

Suspect seen in selfie video

On Monday, police released a video that the suspected gunman apparently took of himself in a market near the nightclub.

Laith Alkhouri, a director at Flashpoint, an American business risk intelligence company tracking terrorist and cyber threats, told CNN the "selfie video" featuring the man in Taksim square was first posted on a pro-ISIS Telegram account before being broadcast by Turkish media.

Alkhouri said that suggests the attacker was part of a network supportive of or linked to ISIS, and that he had shared the selfie footage with them before or after the attack.

Victims from 14 countries

At least 11 victims of the attack on the upscale nightclub were from Turkey, according to Anadolu, while at least 27 victims hailed from 13 other countries, including Lebanon, Iraq, Syria and Canada.

Dozens of people were hospitalized. A handful of the injured were in critical condition.

Witnesses described how the New Year's Eve celebration turned into a bloodbath.

"We were having fun. At first, we thought it was a fight, then there was a lot of gunfire," witness Yunus Turk told CNN.

"After the gunfire, everyone started to run toward the terrace. We ran as well. There was someone next to me who was shot and fell on the floor. We ran away and hid under the sofas."