Turkish police officer checks people near the scene a day after an attack at a popular nightclub in Istanbul. A manhunt is on in Turkey as authorities work to identify the assailant who killed dozens of people in a crowded nightclub during New Year's celebrations Sunday.

ISTANBUL — The Islamic State group today claimed responsibility for the New Year’s attack at a popular Istanbul nightclub that killed 39 people and wounded scores of others.

The IS-linked Aamaq News Agency said the attack was carried by a “heroic soldier of the caliphate who attacked the most famous nightclub where Christians were celebrating their pagan feast.”

It said the man opened fire from an automatic rifle and also detonated hand grenades in “revenge for God’s religion and in response to the orders” of IS leader Abu Bakr al-Baghdadi.

The group described Turkey as “the servant of the cross” and also suggested it was in retaliation for Turkish military offensives against the Islamic State group in Syria and Iraq.

“We let infidel Turkey know that the blood of Muslims that is being shed by its airstrikes and artillery shelling will turn into fire on its territories,” the statement said.

Earlier, Turkish media reports had said that Turkish authorities believed the IS group was behind the attack and that the gunman, who is still at large, comes from a Central Asian nation and is likely to be either from Uzbekistan or Kyrgyzstan.

According to Hurriyet and Karar newspapers, police had also established similarities with the high-casualty suicide bomb and gun attack at Istanbul’s Ataturk Airport in June and was investigating whether the same IS cell could have carried out both attacks.

The gunman killed a policeman and another man outside the Reina club in the early hours of 2017 before entering and firing at an estimated 600 people partying inside with an automatic rifle.

Nearly two-thirds of the dead in the upscale club, which is frequented by local celebrities, were foreigners, Turkey’s Anadolu Agency said. Many of them hailed from the Middle East.

Citing Justice Ministry officials, Anadolu reported that 38 of the 39 dead have been identified and 11 of them were Turkish nationals, and one was a Turkish-Belgian dual citizen.

The report says seven victims were from Saudi Arabia; three each were from Lebanon and Iraq; two each were from Tunisia, India, Morocco and Jordan. Kuwait, Canada, Israel, Syria and Russia each lost one citizen.

The mass shooting followed more than 30 violent acts over the past year in Turkey, which is a member of the NATO alliance and a partner in the U.S.-led coalition fighting against the Islamic State group in Syria and Iraq.