The Islamic State (ISIS) has claimed responsibility for the New Year's Day attack at a popular Istanbul nightclub, killing 39 people and wounding several others.

One man wearing a Santa Claus costume mowed down people using an assault rifle and hand grenades, according to The Blaze. He managed to escape law enforcers and remained at large as of Wednesday. Turkish police believe at least eight more individuals  were involved in the attack.

The ISIS-linked Aamaq News Agency said the attack was carried out by a "heroic soldier of the caliphate" who wanted to open fire at a place "where Christians were celebrating their pagan feast."

The attack was launched in "revenge for God's religion and in response to the orders" of ISIS leader Abu Bakr al-Baghdadi, the news agency said.

The ISIS hates Turkey, describing the country as "the servant of the cross." Sources said the attack was carried out because Turkish military offensives have been relentless against ISIS forces 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," an ISIS statement reads.

Meanwhile, Turkish authorities said Wednesday they have identified the gunman involved in the terror attack but did not give his name or provide his nationality, CNN reported.

Authorities have also detained 20 alleged members of ISIS in connection with Sunday morning's attack at the Reina nightclub, state-run news agency Anadolu reported. Eleven women were reportedly among those arrested.

Police revealed that the suspected gunman even took a "selfie video" of himself near the nightclub before the attack.

Meanwhile, Turkish President Recep Tayyip Erdogan took to Twitter and condemned the "brutal attack" by ISIS. He also asked for God to "have mercy" on his country.

Many people blame Erdogan for what took place since his government ignored the militants when they emerged in 2014 and 2015 when the Syrian civil war broke out.

Erdogan admitted that he and his government bear some responsibility for the New Year's Day terror attack, according to Voices of America.