Russian federal investigators believe an engine fault probably caused the crash of a Russian airliner near the city of Perm with the loss of 88 lives.
The Boeing-737-500, which belonged to Aeroflot subsidiary Aeroflot Nord, caught fire in mid-air as it came in to land on a flight from Moscow.
Lead investigator Alexander Bastrykin linked the crash to "technical failure and a fire in the right engine". The plane's flight recorders have been found and will be analysed.
Giving his preliminary opinion, Mr Bastrykin, head of the federal prosecutors' Investigative Committee, told Russian media there was "much evidence" for the engine fault theory.
Russian Transport Minister Igor Levitin said he had no information to suggest the cause of the crash had been a terrorist attack, or that the plane had exploded in mid-air.
Relatives of some of the dead have arrived in Perm and are being looked after by the local authorities.
There were 82 passengers on board, including seven children, and six crew.
Those killed include General Gennady Troshev, a former commander of Russian forces in Chechnya, and 21 foreign citizens - nine people from Azerbaijan, five from Ukraine and one person each from France, Switzerland, Latvia, the United States, Germany, Turkey and Italy.
Contact with the plane was lost at 0521 Perm time on Sunday as the plane was coming in to land at a height of 1100 metres, Aeroflot said. It crashed on the outskirts of Perm, just a few hundred metres from residential buildings, but no one was hurt on the ground.
Part of the Trans-Siberian railway was shut down as a result of damage to the main east-west train track and the blaze took two hours to extinguish.
One witness says the plane looked like a comet as it came down and burst into a massive fire that lit the whole sky.
Russian federal prosecutors have launched an inquiry to examine whether safety procedures were violated.
Aeroflot says the plane had "a full technical inspection" early this year and was judged to be in a "proper condition".
Sunday's accident was the deadliest involving a Russian airliner since 170 people died in August 2006 when a Tupolev-154 bound for St Petersburg crashed in Ukraine.