The death toll in an accident at a coal mine in western Siberia has risen to 52, state news agencies report, citing rescue workers.
Among the 52 deceased were six rescue workers who died during search operations in the mine. Earlier in the day, more than 30 miners had been declared missing.
An explosion occurred in the mine in the morning for reasons that were not yet known.
According to Russian civil defence teams, a total of 239 workers were rescued from the Listvyazhnaya shaft in the Kuznetsk coal basin.
More than 40 of them are now in nearby hospitals, the governor of Kemerovo Oblast, Sergei Tsivilyov, announced after visiting them.
The mine tunnels were heavily filled with smoke during the rescue operations, local media reported. The search also had to be temporarily interrupted because of the risk of another explosion.
The explosion is said to have occurred at a depth of 250 metres.
Russian President Vladimir Putin expressed his condolences to the relatives of the victims of the "tragedy" and ordered help for the bereaved families and survivors.
"Unfortunately, the situation is not getting easier - there is also a danger to the lives of rescue workers," Putin said.
Investigators said the 47-year-old mine director, his deputy and a department head were arrested on suspicion of violating work regulations.
The area around the mine, which was opened in 1954, was cordoned off. Psychologists attended to relatives. The governor ordered a review of all mines in the region and set a three-day mourning period from Friday to Sunday.
Coal mining work in Russia is considered life-threatening. Due to violations of elementary safety regulations, serious accidents occur regularly.
The explosions are often caused by methane gas. The highly flammable substance accumulates in the shafts and paths underground if ventilation is poor.
There was already an explosion in 2004 in the same mine. It killed 13 people.
In 2007, a total of 107 people were killed in the city of Novokuznetsk in Siberia in the most serious mining accident in Russia in recent years. In 2010, 91 people were killed in two methane explosions in the town of Meshdurechensk in Siberia.