India's Supreme Court says all government allocations of coal reserves to private companies from 1993 to 2009 were conducted illegally, and it will hold a hearing to decide whether to cancel them.

More than 200 coal blocks, or areas of unmined reserves, were allocated during that period to companies for their use in power plants or steel or cement factories.

Companies were allowed to sell excess coal on the open market, but the court said Monday that commercial sales of coal from the reserves must be suspended until it makes its decision.

The court's ruling extends beyond an initial case in which the previous federal government was accused of costing the treasury hundreds of billions of dollars by allocating about 155 coal blocks without competitive bidding in 2004-09.