A safety system monitoring the concentration of methane gas was intentionally disabled at a Kemerovo mine, leading to an explosion that killed 39 miners last month, the state safety watchdog said Wednesday.

The officially stated cause of the accident at the Yubileinaya coal mine is the same as that at the nearby Ulyanovskaya mine, where 110 people died in March.

Konstantin Pulikovsky, head of the Federal Service for Ecological, Technological and Atomic Inspection, said "a rush for super-profits" was the main reason why miners tampered with safety systems, making them indicate lower methane concentrations in mine shafts than was actually the case.

"Experts believe there had been interference with the work of Yubileinaya's safety system," Pulikovsky said. "In particular, someone could have impaired methane gas indicators by simply muffling the equipment with rags."

If there is a buildup of highly explosive methane gas underground, work stops and the miners must be evacuated to the surface and the mine ventilated.

The miners' trade union leaders have said this safety measure is neglected far too often because miners are afraid of losing a day's earnings.

After the March accident at Ulyanovskaya, Yuzhkuzbassugol, which owns the two mines, reduced the proportion of wage packages that comes from bonuses.

Pulikovsky said Yubileinaya was equipped with an unsophisticated, easy to disable, Russian-made safety system.

Steelmaker Evraz Group, which owns 50 percent of Yuzhkuzbassugol, said after the accident at Yubileinaya that it had agreed to acquire the remaining half from the management of the coal-mining firm.