The work-safety watchdog in north Inner Mongolia Autonomous Region has shut down 205 non-coal mines and ordered 136 others to suspend operations in a six-month campaign to boost safety supervision in the resource-rich region, authorities reported Wednesday.

"Illegal operations have prominently existed in Inner Mongolia's non-coal mining sector for years," said a statement issued by the regional government's work safety bureau. "The campaign has ensured safe mining and protected lives."

The authorities did not give breakdowns of the mines forced into closure. Non-coal sector may include mines of iron ore and rare earth, of which Inner Mongolia has rich reserves.

Though no specific illegalities were mentioned, mines in China are commonly shut down for failing to obtain mining licenses or ignoring safety rules.

The work safety watchdog also warned that local government officials would face severe penalties if fatal accidents occur in illegally-operated mines under their watch.

The resource-rich Inner Mongolia also holds the country's largest coal reserves, or 741.4 billion tonnes. It produced 787 million tonnes last year, supplanting Shanxi Province as the top coal producer.

A boom in coal mining has brought prosperity to the region but also raises serious environmental issues. Experts say over exploitation might damage the vulnerable ecology of Inner Mongolia and weaken its role as a natural barrier to prevent sandstorms and desertification from spreading across northern China.

The government has demanded coal mines to meet stricter safety and environmental requirements and launched a region-wide overhaul of the coal mining sector in May.