Rescue workers retrieved the bodies of 78 miners following an explosion at a coalmine in central Siberia, media reported on Tuesday.
Some 200 workers were underground at the Ulyonovsk longwall mine near the city of Novokuznetsk in the region more than 3,000 km east of Moscow when the methane blast occurred on Monday.
The explosion that was preceded by a suspected methane leak has been described as the worst mining catastrophe in the region since 1997.
"We're talking about a very large accident," an official at Russia's Federal Service for Ecological, Technological and Nuclear Control said.
Rescue workers had pulled 83 people alive from the mine and more than 200 rescue workers were searching the collapsed mineshaft for the remaining 40 workers.
At the order of Russian President Vladimir Putin, the country's emergency situations minister, Sergei Shoigu, arrived in Kemerovo with rescue teams from Moscow.
Fourteen rescue teams were on the site, and additional teams were to fly from Krasnoyarsk, approximately 500 km to the northeast.
Rescue work was being hindered by smoke and coal dust blocking the mine's emergency exits, Emergency Situations Ministry spokeswoman Irina Andrianova said.
A part of the mine had also collapsed, further frustrating efforts, Kemerovo Governor Aman Tuleyev told Itar-Tass.
A spokesman for Yuzhkuzbassugol, the facility's owner, said the explosion came about after a sudden and inexplicable increase in methane levels.
Tuleyev, however, said the methane leak occurred after part of the mine's rock cover collapsed.
Kemerovo region prosecutors opened an investigation into neglect of safety procedures around 1430 GMT.
Russian Prime Minister Mikhail Fradkov, speaking from South Africa, said a government commission would investigate the explosion as well.