Turkish police have launched raids in Istanbul and arrested 12 people, as the hunt for an attacker who killed 39 people in a nightclub intensifies.
Deputy Prime Minister Numan Kurtulmus said authorities had fingerprints and a basic description, and vowed to “speedily” identify the suspect.
Some 600 revellers were in the Reina nightclub early on Sunday when the gunman attacked.
The Islamic State (IS) group said it was behind the attack.
There are some reports in Turkish media that the authorities know the man’s identity but have not made it public.
Police have released new images said to be of the suspect but have not yet named him.
Turkish media reports quote police sources as saying he may have been from Uzbekistan or Kyrgyzstan.
Police are investigating whether the suspect belongs to an IS cell blamed for an attack in June on Ataturk airport in Istanbul.
Reports suggest he travelled to Turkey with his wife and two children in November to avoid detection, and that his family are among those detained.
Mr Kurtulmus said the nightclub attack was a “message” against Turkey’s operations in Syria but that they would not be affected.
Turkey launched a military operation in August aimed at pushing back IS and Kurdish forces, with some of the most intensive recent fighting against IS around the northern town of al-Bab.
IS said in a statement that the attack was carried out by “a heroic soldier” and accused Turkey of shedding the blood of Muslims through “its air strikes and mortar attacks” in Syria.
Although IS has been linked to other attacks in Turkey, it has not claimed responsibility before.
Early on Sunday, the gunman arrived at the club by taxi before rushing through the entrance with a long-barrelled gun he had taken from the boot of the car.
Media caption“I was thinking… we are going to die in the bathroom” – attack survivor Tuvana Tugsavult
The attacker fired randomly at people in an assault lasting seven minutes, starting with a security guard and a travel agent near the entrance. Both were killed.
The gunman is reported to have changed clothes before fleeing the chaos.
About two-thirds of those killed were foreign, according to local media.
Victims by nationality
The body of one of those who died has yet to be identified.
At least 69 people are being treated in hospital, officials said, with three in a serious condition.
Barman Mehmet Yilan, 36, said the gunman “stormed in and immediately headed for the people to the left, which is always more crowded… he seemed to know where to go.
“He was shooting randomly but aiming for their upper bodies. He didn’t want to just injure them.”
The nightclub, which sits on the banks of the Bosphorus, is one of Istanbul’s most fashionable venues – popular with foreigners and often frequented by singers and sports stars.
Reported IS attacks in Turkey
20 August 2016: Bomb attack on wedding party in Gaziantep kills at least 30 people, in an attack claimed by IS
28 June 2016: A gun and bomb attack on Ataturk airport in Istanbul kills 41 people, blamed on IS militants
19 March 2016: Suicide bomb kills four people in shopping street in Istanbul. IS blamed
12 January 2016: 12 Germans killed by IS bomber in tourist area of Istanbul
10 October 2015: More than 100 killed at peace rally outside railway station in Ankara; blamed on IS
20 July 2015: 34 people killed in bombing in Suruc, near Syrian border; IS blamed