Russian President Vladimir Putin said that Russia will observe a national day of mourning on Monday after a military plane with 92 onboard crashed in the Black Sea on Sunday with no sign of survivors.

"Tomorrow Russia will declare a national day of mourning," Putin said on state television.

The Russian Defense Ministry said one of its TU-154 Tupolev planes had disappeared from radar screens at 5:25 am, two minutes after taking off from Adler in southern Russia, where it had stopped to refuel from Moscow, on its way to Syria.

Major General Igor Konashenkov, a ministry spokesman, told reporters that nobody had survived.

"The area of the crash site has been established. No survivors have been spotted," he said.

An unnamed ministry source told Russian news agencies no life rafts had been found, while another source told the Interfax agency that the plane had not sent an SOS signal.

The jet, built in 1983, had been carrying 84 passengers and eight crew members.

At least 60 were members of the Alexandrov Ensemble, better known internationally as the Red Army Choir, and were being flown to Russia's Hmeymimair base in Syria to entertain troops in the run-up to the new year. Nine Russian reporters were also on board as well as military servicemen. Konashenkov said fragments of the plane had been found at a depth of about 70 meters in the Black Sea about 1.5 kilometers off the coast near the city of Sochi.

"The search operation is continuing," said Konashenkov. "Four ships, four helicopters and a plane and a drone are working in the area," he said, adding that a military commission had flown to Sochi to investigate.

Konashenkov said four bodies had been recovered from the sea. Russian news agencies cited a higher figure.

Russia's RIA news agency, citing an unidentified security source, said preliminary information indicated that the plane had crashed because of a technical malfunction or pilot error. Another source told Russian agencies that the possibility of a militant act had been ruled out. The weather had been good.

Konashenkov said the plane had last been serviced in September and undergone more major repairs in December 2014.He said the pilot was experienced and that the plane had about 7,000 flying hours on its clock.

Kremlin spokesman Dmitry Peskov told reporters it was too early to say what had caused the crash. Russian military investigators said they had opened a criminal investigation.

The last big TU-154 crash was in 2010, when a Polish jet carrying Poland's then-president Lech Kaczynski and much of Poland's political elite crashed in western Russia, killing everyone on board.

On Dec 19, a Russian military jet crashed in Siberia with 39 people on board as it tried to make an emergency landing near a Soviet-era military base. Nobody was killed, though 32 people were flown to hospitals.