UPDATE: 12/29 8:32 a.m.
Russian investigators announced Thursday that they found no evidence of an explosion or fire on the military plane that crashed into the Black Sea early Sunday morning.
So far, terrorism hasn't been ruled out as a cause, but investigators said it's unlikely.
Sergey Bainetov, the Russian Air Force deputy head of flight safety, told CNN the full investigation could take a month.
So far investigators have gathered more than 2,000 fragments of the plane and recovered 19 bodies.
Transport Minister Maxim Sokolov told CNN the plane likely fell apart after it hit the water's surface.
ORIGINAL STORY: So far 13 bodies and more than 150 pieces of debris have been recovered in the aftermath of Sunday's Russian military plane crash, CNN reports, citing the Itar-Tass news agency.
The plane crashed into the Black Sea early Sunday morning shortly after taking off from Sochi with 92 people on board, including members of the Russian army choir.
On Monday, Kremlin spokesman Dimitri Peskov told reporters terrorism was not suspected as the cause of the crash.
Instead, Peskov said the plane likely crashed due to mechanical failure or pilot error.
The Russian Investigation Committee launched a criminal investigation to see if anyone violated the flight safety or preparation rules.
Since the crash, 3,500 people, 43 ships and 182 divers have been deployed to search for bodies and debris, according to ABC News.
Russian President Vladimir Putin declared Monday a national day of mourning.
Human rights activist among dead
Searchers have been using data from radio location equipment to narrow their search and locate the crash site.
Russia's defense ministry said Monday that eight crew members, eight soldiers and more than 60 members of the Alexandrov Ensemble choir were among those feared dead. In addition, CNN reports that the famous Russian human rights activist, Liza Glinka, was also on board.
Wreckage a mile offshore
"Military personnel of the Southern Military district keep examining the shoreline to find and collect the bodies, debris of the plane and personal belongings of passengers," Russia's defense ministry told CNN.
All of the bodies and debris that were found as of Monday morning were flown to Moscow, where scientists will conduct DNA tests. CNN reports that divers found the Tupolev Tu-154 plane's fuselage approximately a mile offshore.
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