The Industry and Energy Ministry's technical standards agency said 33 coal mines had been closed, including 29 in the coal-rich region of Kuzbass.
The failure of the mine ventilation system at Ulyanovskaya is believed to have caused the strong build-up of methane that led to the blast, the Associated Press reported.
The AP said Russian news reports claimed Ulyanovskaya miners may have deliberately disabled methane gas monitors and detectors to avoid a slowdown in operations, leading to possible wage cuts.
