At least four miners died Sunday when fumes filled the shaft where they were working in Russia's main coal-producing region, reports said.
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-Novosti and Itar-Tass news wires said.
Also, 69 miners managed to escape, the reports said.
Russia's coal mines have a poor safety record and President Vladimir Putin warned operators to improve standards as he announced a multibillion-dollar investment in the sector last year.
