Anti-terror police made their first arrests over the attack, which unleashed scenes of panic among party-goers at one of Istanbul's swankiest venues and killed mostly foreign tourists.
The shooting took place just 75 minutes into 2017 after a bloody year in Turkey in which hundreds of people were killed in violence blamed on both IS jihadists and Kurdish militants.
In a statement circulated on social media, the jihadist group said one of the "soldiers of the caliphate" had carried out the attack on the Reina nightclub.
This is the first time IS has issued a clear and undisputed claim for an attack inside Turkey, despite being blamed for several major strikes in Istanbul and other cities over the last year.
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It has in the past however claimed individual assassinations of Syrian anti-jihadist activists in the south of Turkey.
The IS statement said the attack was in response to Turkey's military intervention against the jihadists in war-ravaged Syria the military presses a four-month incursion to oust jihadists from the border area.
In the last few weeks, the forces have encountered fierce opposition from the jihadists around the town of Al-Bab. The army said Turkish war planes launched new air strikes around Al Bab.
Arriving by taxi at the plush Reina nightclub on the shores of the Bosphorus, the gunman produced a weapon, reportedly a Kalashnikov, and shot dead a policeman and civilian at the entrance.
According to the Hurriyet daily, the gunman then fired off four magazines containing a total of 120 bullets around the club, as terrified guests flung themselves into the freezing waters of the Bosphorus in panic.
Interior Minister Suleyman Soylu said yesterday that intense efforts were under way to find the gunman, and expressed hope that he would be captured soon.
Late yesterday, police rushed to Istanbul's Kurucesme district after a tip-off but the operation did not produce any arrest.
"The danger continues," wrote columnist Abdulkadir Selvi in Hurriyet.
"So long as this terrorist is not seized we do not know when and where a massacre could take place.