An official inquiry into a Russian coal mine blast in Siberia that killed 108 people says the explosion was caused by someone tampering with safety equipment.

Konstantin Pulikovsky, head of the industrial agency, Rostekhnadzor investigating the tragedy, Tuesday said the mine's methane gas detection system was not working.

He said the system is designed to automatically cut off the electricity supply to the mine if dangerous levels of methane gas are detected.

The March 19, 2007 methane gas blast at the Ulyanovskaya mine was one of Russia's worst mining disasters.

Russia's aging coal mines are notoriously unsafe, with many lacking the latest equipment. But the Ulyanovskaya mine was opened in 2002, making it one of the more modern mines.

Some information for this report was provided by AFP and AP.