A gas leak from a Siberian coal mine has left at least 52 dead, Russian news agencies said, including six rescuers who were sent to try to get out dozens of still missing men.
It is one of the worst mining disasters in Russia since Soviet times.
The regional commission of inquiry said three people, including the manager of the Listvyazhnaya mine and his deputy, were arrested for violating industrial safety rules.
He said miners suffocated when a ventilation shaft filled with gas.
State television said prosecutors believed there had been a methane explosion.
The dead included 11 minors already confirmed killed, 35 who had been reported missing and the six rescuers.
Dozens of people have been treated in hospital, at least some of them for smoke inhalation. Four were in critical condition.
The coal-producing region of Kemerovo, about 3,500 km east of Moscow, has suffered fatal mining accidents for years.
Listvyazhnaya mine is part of SDS-Holding, owned by the Union of Siberian Private Enterprises. The owner did not immediately comment.
Some 285 people were inside the mine when smoke spread through the ventilation duct, the emergency ministry said.
Authorities said 239 had reached the surface.
President Vladimir Putin said he had spoken to the governor and emergency officials, and the Kremlin said it had ordered the emergency minister to visit the region to help.
Kemerovo has declared three days of mourning.
In 2007, the region was the scene of the worst mining accident since the collapse of the Soviet Union when an explosion at the Ulyanovskaya mine claimed the lives of more than 100 people.
In 2010, explosions at the region’s Raspadskaya mine killed more than 90 people.
Australian Associated Press