So-called Islamic State says it was behind the new year attack on a Turkish nightclub that killed 39 people.
The group said in a statement it was carried out by “a heroic soldier”.
At least 600 revellers were celebrating in the early hours of Sunday at Istanbul’s Reina nightclub when the gunman began firing indiscriminately, discharging some 180 bullets.
The gunman is still at large and a manhunt is under way. Police say they have made 12 arrests so far.
Late on Monday, Turkish media said special forces police backed by a helicopter launched an operation on a house in the Zeytinburnu district following a tip but that the attacker was not found.