BEIJING  - China's state planner and market regulator have jointly launched an investigation into coal prices and will crack down on speculation and hoarding, the country's economic planning agency said on Friday.

Reuters last week reported that a team of inspectors from five government departments, including the National Development and Reform Commission (NDRC) planning agency and the state market regulator, visited major coal hubs in northern China to investigate inventories and illicit hoarding.  

Physical prices for thermal coal in the 5,500 kilocalorie/kilogramme grade have been hovering around 900 yuan ($139.63) per tonne since early May, a record high. That triggered at least three leading Chinese coal pricing indices to suspend publication of daily assessments in a bid to stabilise prices.  

"(The soaring prices) have added a burden on downstream sectors, and are having a negative effect on the development of the real economy," the NDRC said in a statement.

Coal-fired power plants, bearing the brunt of the price spike as major thermal coal users, are rushing to build up inventory ahead of peak summer demand.

"The government will closely monitor commodity prices ... get to know the operation situation at relevant market participants, check abnormal trading and speculation, as well as crack down on hoarding and driving up prices," the NDRC said in its statement.

($1 = 6.4455 Chinese yuan renminbi)

(Reporting by Muyu Xu and Dominique Patton; Editing by Jacqueline Wong and Kenneth Maxwell) ((muyu.xu@thomsonreuters.com; +86 10 56692117;))