Russian officials say they can't rule out terrorism after a Russian military passenger jet plunged into the black sea.
It's believed all 92 people on the Syria-bound flight have been killed.
The search for victims continues after a Russian passenger plane crashed into the Black Sea on Sunday.
The Russian Defence Ministry says one of its TU-154 [T-U-1-5-4] Tupolev planes disappeared from radar two minutes after taking off from Sochi, where it had stopped to refuel from Moscow, on its way to Syria.
Fragments of the plane and at least 10 bodies have been located within kilometres of the Black Sea coastline.
Defence Ministry spokesman Major General Igor Konashenkov says the search for the remaining passengers and crew members is ongoing.
"All Defence Ministry and other federal ministry rescue services are engaged in the search. The TU-154 was carrying Russian military servicemen, the Alexandrov orchestra - which was going to perform during New Year's celebrations at our Hmeimim airbase - and nine Russian journalists."
Russian authorities say they are not ruling out any possible causes for the crash, including a terror attack.
But Russian Transport Minister Maxim Sokolov insists it is too early to speculate.
"The investigative committee is looking into the (possible) reasons (of the crash). Of course an entire spectrum (of causes) and all possible causes which might have led to the crash are being considered, but it is too early to talk about it.”
Mr Sokolov says, despite recovery efforts, no survivors have been found.
“We have launched a search and recovery operation. Unfortunately, we haven't found any survivors. And I, on behalf of the government committee, want to express my sincerest condolences to all relatives and loved ones of those who died in this crash."
Mourners in Moscow have gathered with flowers and tributes to honour victims of the crash, including dozens of Red Army choir members on their way to perform a New Year's concert at the Russian military base in Syria.
Chorister Vadim Ananiev says he was meant to be on the plane.
"My child was born. He's just a few months old. The eldest is 10. The middle one is five. My wife just couldn't cope alone, so I asked my choir director for understanding and he agreed. As a result I am standing in front of you, but I was supposed to be on this flight. I was woken up by a phone call and was told what had happened. I just can't believe what's happened. We need time to comprehend it. My wife is crying. My kids don't understand. Now I just want to go to church and pray for my colleagues."
Russian President Vladimir Putin has declared a national day of mourning on December the 26th to honour victims and their families.
"First of all I would like to express the most sincere condolences to the families of our citizens killed this morning in an air crash over the Black Sea. The government was asked to form a commission which will be headed by the transport minister. A thorough investigation of the causes of the crash will be carried out and everything will be done to support the families of those killed. A national day of mourning will be held in Russia tomorrow."
