Zimbabwe has drastically increased exploration fees for diamonds and coal, in an effort to discourage companies from speculating on mining claims, state media reported on Wednesday.

The state-owned Herald newspaper said the exploration fee for diamonds had increased twenty-fold, to $1 million, while the coal fee went up five-fold to $100,000 from $20,000.

Mines Minister Obert Mpofu could not be reached for comment.

The Zimbabwe Chamber of Mines said the increase was unexpected but would not say whether it would impact new investment in the resource-rich nation.

We were not consulted about it and this is quite a hefty increase, Chris Hokonya, the chamber's chief executive, told Reuters.

The government has said many companies hold mining claims for speculation and the increase in exploration fees is seen as discouraging the practice.

Global miner Rio Tinto is just one of the foreign companies mining diamonds in the southern African nation.

The government last year announced it would nationalise all alluvial diamond mining operations, mostly in the eastern Marange district, while handing management contracts to private companies.