China's State Administration for Market Regulation has conducted investigations on activities of bidding up coal prices, the administration said Friday.

Three investigation teams have been sent to provincial-level regions of Shanxi, Inner Mongolia and Shaanxi, the country's major coal-producing regions, to advance regulations on coal price gouging.

After investigation, a total of 18 coal enterprises were suspected of driving up coal prices, and three trading centers were suspected of not adopting government pricing, the administration said.

The administration will continue to strengthen supervision over coal prices and guide the prices to operate within a reasonable range.