ISIL has claimed responsibility for the attack on a nightclub in Istanbul that killed 39 people on New Year's Eve.

The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group released on Monday a statement claiming responsibility for the raid.

"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 the Christians celebrate their apostate holiday," the statement said.

The announcement came as a manhunt was under way in Turkey for at least one assailant who attacked those celebrating New Year at the Reina nightclub.

Shortly after the ISIL claim, AFP news agency citing local media said that police have detained eight suspects over the attack.

The Dogan news agency said police were pressing on with operations after making the first arrests over the attack.

The Reina lies on the shore of the Bosphorus Strait and is one of Istanbul's best-known nightclubs, popular with locals and tourists alike. During the attack, some partygoers who managed to flee jumped into the freezing cold Bosphorus strait to escape harm.

Al Jazeera's Mohammed Jamjoom, reporting from Istanbul, said: "The ISIL statement doesn't say whether the attacker was trained by ISIL or simply pledged allegiance to the group and carried out the attack alone.

"There had been consensus emerging behind the scenes, and reports in Turkish media, indicating officials believed ISIL was behind the attack."

He added that the mood in the busy Turkish city was "sombre and sad".

Turkey is currently in a state of emergency.

"People are very scared. This is the fourth attack to hit Turkey in less than a month ... There is a sense here in Istanbul of astonishment as to how this could have happened at a time when there were tens of thousands of officers on the streets to prevent an attack on New Year's Eve."

As well as the 39 dead, about 70 others were wounded and three of those people remain in critical condition, Binali Yildirim, Turkey's prime minister, said on Sunday.

Interior Minister Suleyman Soylu described the attack as a "massacre, a truly inhumane savagery".

READ MORE: Istanbul - Victims of Reina nightclub attack identified

Foreigners, including many nationals of Arab countries, were among the dead, officials said.

Eleven of the dead were Turkish nationals and one was a Turkish-Belgium dual-national. Seven victims were from Saudi Arabia and had travelled to Istanbul for New Year's Eve celebrations. Three of the dead were from Lebanon and Iraq each. Two nationals from Tunisia, India, Morocco and Jordan were killed, and Kuwait, Canada, Israel, Syria and Russia lost one citizen in the attack.

One victim remains unidentified.

TIMELINE: Attacks in Turkey

Security measures had been heightened in major Turkish cities, with police barring traffic leading up to key squares in Istanbul and Ankara.

In Istanbul, 17,000 police officers were put on duty, some disguised as Santa Claus and others as street vendors, Turkey's Anadolu news agency reported.

Turkey, part of the US-led coalition against ISIL, faces multiple security threats, including fallout from the war in neighbouring Syria.

It has seen repeated attacks and bombings blamed on ISIL, as well as fighters from the Kurdistan Workers' Party (PKK) in recent months.