Fourteen suspects are now in custody over a massacre that targeted a popular nightclub in Istanbul on New Year's Eve, killing 39 people and wounding dozens of others.

Turkey's state-run news agency, Anadolu said that an ongoing series of tips or sightings from citizens led to half a dozen more detentions on Tuesday, as the main suspect, who allegedly carried out the attack, remains at large.

The suspects continue to be questioned at Istanbul's main police headquarters, media said, adding that security experts say the killer was an experienced assassin. Turkish police have released a photo of him.

The release of the image on Monday came as Deputy Prime Minister Numan Kurtulmus said that the country's state of emergency, which was already in place at the time of the attack, would be extended for as long as needed.

The parliament voted on the issue on Tuesday to extend it for another three months, following a six-month mandate.

Turks mourn the dead (2:22)

Kurtulmus also said authorities were close to identifying the gunman after obtaining his fingerprints and a description of his appearance.

The attack was claimed by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

TIMELINE: Attacks in Turkey

"Information about the fingerprints and basic appearance of the terrorist have been found. In the process after this, work to identify him swiftly will be carried out," Kurtulmus told a news conference.

He said it was clear that Turkey's military incursion into Syria, launched in August, had annoyed armed groups and those behind them, but said the offensive would continue until all threats to Turkey were removed.

Turkey sent tanks and special forces into Syria just over four months ago to push back ISIL fighters from its border and prevent Kurdish fighters from taking ground in their wake.

Kurtulmus also said Sunday's attack bore significant differences to previous attacks in Turkey and that it had been carried out to create divisions within Turkish society.

Newspaper reports said the attacker was thought to be from a Central Asian nation [Dogan News Agency/AFP]

Al Jazeera's Mohammed Jamjoom, reporting from Istanbul, said that citizens he spoke to in various parts of Istanbul were concerned that those types of attacks might become more common in the future.

He said: "They are still shocked. It is astounding for them that an attack of this magnitude could happen at such a high-profile club, at a time this country is under a state of emergency, and tens of thousands of security officers spread out throughout the city were trying to prevent such an attack from happening on New Year's Eve."

Foreigners killed 

The assailant, who is believed to be of Central Asian decent, slipped from the scene of the attack at the Reina club early on Sunday, taking advantage of the chaos that ensued after he opened fire.

Turkish media ran on Tuesday a selfie-style video of a man they say is the gunman. Broadcast on Turkish television, the footage shows the alleged attacker filming himself at the central Taksim Square. It was not immediately clear if it was filmed before the attack.

As the operation to close in on the suspect continued, Turkish victims were laid to rest as families of those from other countries arrived in the country to take their loved ones' remains back home.

The majority of those killed were foreigners, including many Arab nationals.

The victims included citizens of Turkey, Saudi Arabia, Lebanon, Iraq, France, Tunisia, India, Morocco, Jordan, Kuwait, Canada, Israel, Syria, Belgium, Germany and Russia.

Sisters of Lebanese Elias Wardini, who was killed in the overnight Istanbul attack, mourn at their house in Lebanon [AP]

Source: Al Jazeera and news agencies