The bodies of 11 victims and more than 150 plane fragments have so far been recovered from a Syria-bound Russian jet that crashed in the Black Sea on Sunday (25 December).
It comes as Russia held a day of mourning on Monday for the 92 people aboard flight Tu-154 – none of whom are believed to have survived.
In addition to eight crew members and several journalists, the passengers included 65 members of the Russian military choir Alexandrov Ensemble heading to the Latakia airbase in Syria for a special Christmas Day performance.
Renowned Russian humanitarian and charity worker Elizaveta Glinka, better known as Dr Liza, is also believed to be among the dead. She was transporting medical supplies to Syria, on behalf of the UN's Human Rights Council.
Major-General Igor Konashenkov, a Defense Ministry spokesman, told Reuters that more than 3,500 people are currently involved in the search.
He said that 39 ships, five helicopters, a drone and more than 100 divers were involved.
The plane crashed roughly seven minutes after take-off from Sochi Airport, after stopping there for an unexpected refuel, and it is believed the black box is close to being recovered.
"The projected site of the collision has been established, large parts of the aircraft's fuselage may be located there," a source told Russian news agency Tass.
Russian Transport Minister Maxim Sokolov, who is one of the lead investigators into the crash, said terrorism is not thought to be the cause of the disaster, however it has not been ruled out at this stage.
"The main versions [for the crash] do not include the idea of a terrorist act," Sokolov told a news conference in Sochi, the RIA news agency reported.
"So we are working on the assumption that the reasons for the catastrophe could have been technical or a pilot error.
"I will emphasise, however, that this will be established by investigators as well as special technical commission of the Russian Defense Ministry."