Two deadly blasts at the Raspadskaya coalmine, which killed at least 11 people, was caused by methane, investigators said on Sunday.
They earlier said it either methane-air mixture or pulverized coal exploded at the mine.
The region's administration said 12 miners were killed, but the information is yet to be officially confirmed.
A total of 41 miners were injured in the blasts. But rescuers fear that casualties might rise as 84 people, including 20 rescuers, remain unaccounted for after the second blast.
"We have already brought seven bodies to surface, they are being taken to morgue for identification," a spokeswoman for the regional investigation department said.
The families of those killed are likely to receive 1 million rubles (almost $33,000) in compensation from the mine's owner, along with compensations paid by the state and regional authorities, a spokesman for the regional administration said.
"Families of the deceased, children of miners will get all the necessary assistance. The government has already discussed the issue with the mine's owners," Sergei Cheremnov said.
MOSCOW, May 9 (RIA Novosti)