The Islamic State group has claimed responsibility for the mass shooting on New Year's Eve in a packed Istanbul nightclub that left 39 dead, as Turkish authorities continued their hunt for the attacker Monday morning. The Associated Press reported that police have detained eight people, but the gunman is not thought to be among them.The claim, released on the encrypted Telegram messaging app and circulated on Twitter, praised a "soldier of the caliphate" for carrying out the attack on a target date when "Christians celebrate their apostate holiday."Describing Turkey as "the servant of the cross," the statement said the attack was carried out under the orders of leader Abu Bakr al-Baghdadi, and suggested it was a response to Ankara's military activities against IS. Turkey is a key member of the U.S.-led anti-IS coalition, and has forces in northern Syria and Iraq involved in operations against the jihadi group.The claim of responsibility was unusual: While IS has been blamed for a number of mass-casualty attacks on civilian targets in Turkey in the past 18 months, it has not officially claimed any before. "The apostate Turkish government should know that the blood of Muslims shed with airplanes and artillery fire will, with God's permission, ignite a fire in their own land," the statement said.Read more on VICE News.