A fire at Niger's justice ministry has destroyed files on anti-corruption cases against a number of judges.

The fire in the capital, Niamey, broke out early Tuesday, seriously damaging the justice ministry building and many paper archives inside.

Authorities say the documents included evidence collected to prosecute allegedly corrupt magistrates. Some of the information had been collected from a phone hotline set up as part of the investigation.

Police are investigating whether the fire was accidental or set on purpose.

Niger, like many African countries, has battled chronic corruption among officials. The government of President Mahamadou Issoufou has said stamping out graft is a top priority.