Russian investigators do not regard "a terrorist act" as one of the main theories behind the crash of a military plane in the Black Sea, the Kremlin said.
All 84 passengers and eight crew members on board the plane operated by the Russian military are believed to have died when it crashed two minutes after taking off in good weather from the southern Russian city of Sochi on Sunday morning.
"[Investigators] are considering all versions of events," Kremlin spokesman Dmitry Peskov told reporters on a conference call on Monday.
"It is still too early to say. But the version that it was a terrorist act is nowhere near the top of the list."
Vigils were held in Russia on Monday after Russian President Vladimir Putin declared a day of mourning.
Following the crash, Russia launched a search operation that involved more than 45 ships and 3,500 people, including 135 divers flown in from across Russia, sweeping a vast crash site at sea and along the shore, according to the defence ministry.
Five helicopters and drones were being used to help spot bodies and debris.
Two deep-water submersibles arrived on Monday in Sochi to aid the operation, which went on all through the night thanks to powerful searchlights.
The Black Sea search area, which covers over 10 square kilometers, is plagued by underwater currents that can carry debris and body fragments into the open sea.
The search party has not yet found the plane's black boxes, Emergency Situations Minister Vladimir Puchkov told Russian news agencies.
The plane, belonging to the defence ministry, was taking Russia's famed choir, the Alexandrov Ensemble, to a New Year's concert at Hemeimeem air base in Syria's coastal province of Latakia.
One singer, who did not get on the plane due to the recent birth of his child, said he was devastated at the loss of so many talented colleagues.
"I have lost my friends and colleagues, all killed, all five soloists. I feel in complete disarray," Ananyev told the AP news agency.
"It is such a shame. I have known these people for 30 years. I know their wives and children. I feel terrible for the children and for all that I have lost."
Mourners lit candles and brought flowers to Channel One and NTV, whose TV journalists were going to Syria to cover the concert, and to a charity founded by Dr Yelizaveta Glinka, who was on the plane bringing medicines to Syria.
Source: Al Jazeera and news agencies