Turkish security forces are searching for the gunman who killed 39 people and wounded more than 60 others at the Reina nightclub early on Sunday.
Reina is a popular nightclub in Istanbul's Ortakoy district, and at the time of the incident around 500 to 600 people were thought to be celebrating the new year.
Foreigners including an Israeli woman, people from Saudi Arabia, Lebanon and Jordan were among those killed.
"I have heard stories that the terrorist was wearing a Santa costume. That is not correct. The attacker had a weapon, he killed two people outside of the club. He entered the club and at random, he started shooting. He left his weapon at the scene," Turkish Prime Minister Binali Yildirim said during a visit to one of the wounded men.