All possible causes for the crash of a military jet which plunged into the Black Sea are being considered, including a terror attack, according to Russia's transport minister.
All 92 people on board the Russian military Tu-154 died after it came down shortly after take-off near the resort town of Sochi.
Minister Maxim Sokolov said an "entire spectrum" of causes were being investigated, and added it was premature to speculate.
Viktor Ozerov, head of the Russian parliament's defence committee, had earlier told state media that he "totally excludes" terrorism as a cause of the crash.
He said it could have been caused by a technical malfunction or crew error.
The plane was carrying 64 members of the renowned military choir and dance band, the Alexandrov Ensemble, including its conductor Valery Khalilov.
The ensemble, better known as the Red Army Choir, was heading to Syria to give a concert at a Russian air base.
Nine members of the media were among the 84 passengers on board.
Eight crew were also on the plane.
Among the dead is Dr Yelizaveta Glinka, a renowned aid worker, who has been honoured by President Putin.
At least four bodies are reported to have been recovered from the crash site so far.
President Vladimir Putin has ordered an investigation into the cause of the crash.
He also offered deepest condolences to the victims' families, according to a Kremlin spokesman.
The aircraft was a Tu-154, a Soviet-designed three-engine airliner.
It disappeared minutes after taking off over the Black Sea.
The plane had departed at 5:40am local time (0240 GMT) from Adler, south of Sochi, where it had stopped to refuel after taking off from Moscow.
Fragments of the plane have been found about 1.5km (0.93 miles) from the Russian coast.
Some personal documents from those on board have also been recovered.
The plane was flying to Russia's Hmeimim airbase outside the coastal Syrian city of Latakia, the ministry said.
The Tu-154 aircraft has been involved in a number of accidents in the past.
In April 2010 the-then Polish president Lech Kaczynski was killed when a Tu-154 airliner crashed near Smolensk in western Russia.
