MOSCOW At least four miners died when fumes filled the shaft where they were working in Russia's main coal-producing region on Sunday, Russian news agencies reported.
Searches for another four missing men had to be suspended after levels of methane in the mine in the Kuznetsk Basin reached dangerous levels, the RIA and ITAR-Tass news wires said. Sixty-nine miners managed to escape, they added.
Russia's coal mines have a poor safety record and President Vladimir Putin warned operators to improve standards as he announced a multi-billion dollar investment in the sector last year.
Moscow has ambitious plans to boost coal output despite weak world prices and competition from cheap natural gas resources from shale.
The Kuznetsk Basin in west Siberia, about 3,500 km (2,200 miles) east of Moscow, mined 192 million tonnes of coal in 2011, about 57 percent of Russia's total output.
(Writing by Melissa Akin and Maria Kiselyova)