The so-called Islamic State group has claimed responsibility for the New Year's Day shooting in a packed Istanbul nightclub that left 39 people dead.
The deadly attack was carried out by a lone gunman who remains at large.
The jihadist group described the Reina nightclub, where many foreigners as well as Turks were killed, as a gathering point for Christians celebrating their "apostate holiday".
It said the attack was revenge for Turkish military involvement in Syria.
"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 IS declaration said.
There was no immediate comment from Turkish officials.
The militant group has been blamed for at least half a dozen attacks on civilian targets in Turkey over the past 18 months; but, other than assassinations, this is the first time it has directly claimed any of them.
It made the statement on one of its Telegram channels, a method used after attacks elsewhere.
NATO member Turkey is part of the US-led coalition against IS and launched an incursion into neighbouring Syria in August to drive the radical Sunni militants from its borders, sending in tanks and special forces backed by fighter jets.
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Nationals of Saudi Arabia, Lebanon, Morocco, Libya, Israel,India, Canada, a Turkish-Belgian dual citizen and a Franco-Tunisian woman were among those killed at the nightclub on the shores of the Bosphorus waterway.
25 of the dead were not Turkish, according to the state-run Anadolu news agency.
All of those killed died from gunshot wounds, with some shot at a very close distance or even point-blank range, according to a forensics report quoted by Milliyet newspaper.
Police distributed a hazy black-and-white photo of the alleged gunman taken from security footage. State broadcaster TRT Haber also said eight people had been detained in Istanbul.
The authorities believe the attacker may be from a Central Asian nation and suspect he had links to IS, the Hurriyet newspaper said.
It said he may be from the same cell responsible for a gun-and-bomb attack on Istanbul's main airport in June, in which 45 people were killed and hundreds wounded.
The attack at Reina, popular with Turkish celebrities and wealthy visitors, shook Turkey as it tries to recover from a failed July coup and a series of deadly bombings, some blamed on IS, others claimed by Kurdish militants.
Around 600 people were thought to be in the nightclub when the gunman killed a policeman and civilian at the door, forcing his way in before opening fire with an automatic assault rifle. Witnesses said he shouted "Allahu Akbar" (God is Greatest).
Some at the exclusive club jumped into the Bosphorus after the attacker opened fire at random just over an hour into the new year. Witnesses described how he shot the wounded as they lay on the ground.
Europe on high alert since Berlin attack
Security services had been on alert across Europe for new year celebrations following an attack on a Christmas market in Berlin that killed 12 people.
Only days ago, an online message from a pro-IS group called for attacks by "lone wolves" on "celebrations, gatherings and clubs".
In a statement hours after the shooting, President Tayyip Erdogan said such attacks aimed to create chaos and destabilize the country.
Four months into its operation in Syria, the Turkish army and the rebels it backs are besieging the IS-held town of al-Bab.
Mr Erdogan has said he wants them to continue to Raqqa, the jihadists' Syrian stronghold.
Turkey has also been cracking down on IS networks at home.
147 people have been detained and 25 formally arrested in counter-terrorism operations since St Stephen’s Day, according to the interior ministry.
The New Year's Day attack came five months after a failed military coup, in which more than 240 people were killed, many of them in Istanbul, as rogue soldiers commandeered tanks and fighter jets in a bid to seize power.
More than 100,000 people, including soldiers and police officers, have been sacked or suspended in a subsequent crackdown ordered by Mr Erdogan, raising concern both about civic rights and the effectiveness of Turkey's security apparatus.
