The Islamic State group on Monday claimed responsibility for the New Year’s Day attack at an Istanbul nightclub that killed 39 people and injured several others. Turkish officials are still on the lookout for the shooter and have detained eight people in connection with the attack, AP reported.

Using Nashir News, the extremist group issued a statement that said, “In continuation of the blessed operations that the 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 Christians celebrate their apostate holiday,” Reuters reported.

Officials said the shooter may be from a Central Asian nation. Police have been circulating a visual of the alleged attacker, retrieved from security footage.

At least 600 people were at the nightclub’s New Year’s Eve party when the attacker, dressed as Santa Claus, rained bullets on them at the Reina Club in Turkey’s Ortakoy area. The club is located on the Bosphorus river, and several people had jumped into the water to escape. They were later rescued by the police. Citizens of Saudi Arabia, Morocco, Lebanon, Libya, Israel, India, a Turkish-Belgian dual citizen and a Franco-Tunisian woman were among those killed.

Security officials were ordered to be on high alert across Europe, particularly during the New Year celebrations. The agency said an online message from a pro-Islamic State group urged supporters to launch “lone wolf attacks” on celebrations.

The incident followed several attacks in December in Turkey, including twin blasts at a stadium in Istanbul that killed 38 people and injured 166 others and the assassination of the Russian ambassador on December 19.

The Islamic State and other radical groups have targeted Turkey, a North Atlantic Treaty Organisation member that is part of the United States-led coalition against the extremist faction in Syria.