Guinea's military government has cancelled 129 minerals exploration permits, it said in a statement late on Monday, as the West African nation tightens control over its assets.

A senior official at the Ministry of Mines said the decision was taken to free unused resources for other investors.

"We've simplified it by digitising the whole system, which can now be better controlled," the official told Reuters, speaking on condition of anonymity.

It wasn't immediately clear whether any significant investments would be affected by the move.

Mining licences revoked

A second Guinean ministry official said most of the cancelled permits were to identify gold deposits and that the assets had been returned to the state.

Guinea this month retracted 51 mining licences that were being underutilised or hadn't begun operating. Those licenses concerned bauxite, gold, diamond, graphite and iron concessions.

It had previously moved to withdraw bauxite licences belonging to Kebo Energy SA and Emirates Global Aluminium.

Guinea is home to the world's largest reserves of bauxite, the main ore used to produce aluminium. China is a major operator in the country.

The effort to improve control over its resources comes as other military governments in Niger, Mali and Burkina Faso have also cracked down on foreign miners and sought to boost revenue from production.