Russia rules out explosion in military plane crash
Terrorism has not been ruled out as the cause of the crash, but it is not a primary line of investigation, the air force's deputy head of flight safety, Sergey Bainetov, told the state-run TASS news agency.
The Defense Ministry has said there are probably no survivors.
Bainetov said the full investigation would take a month.
"The search operation continues as we need to recover more fragments to conclude the investigations," he said.
Transport Minister Maxim Sokolov said it has been established that "the plane almost completely fell apart after it hit the water surface and the sea shore, which has naturally complicated the search operation," Russia's Sputnik news reported.
More than 130 square kilometers of the sea have been examined. Teams have found 2,000 fragments of the plane, 19 bodies and 230 body parts, Sputnik reported.
The Tupolev Tu-154 was carrying 84 passengers and eight crew members when it crashed.
Both black boxes -- the cockpit voice recorder and flight data recorder -- have been recovered and are being studied.
Those on board included 64 musicians from the army's official choir, the Alexandrov Ensemble; nine reporters; the head of the Spravedlivaya Pomoshch charity, Elizaveta Glinka; two federal civil servants; and eight crew members.
Read: The 'Red Army' choir loved by Russia
The choir was flying to Syria to perform for Russian air force pilots during the holiday season, the Defense Ministry has said.
Glinka was taking medicine and other supplies to a local hospital in Syria, her colleague and friend Dr. Sergey Kurkov told CNN affiliate RBC.
The plane had taken off from Moscow and was headed to the Russian Hmeymim air base in Latakia, Syria, where Russia has a large military presence. En route to Syria, the plane landed in Sochi to refuel.