Dozens of opposition members have been arrested in Niger accused of plotting a "military coup" in the west African nation, Interior Minister Hassoumi Massaoudou told AFP on Saturday.

Close to 40 allies of parliament speaker Hama Amadou were detained this week for planning "a campaign of terror", Massaoudou said, charging that some were found with petrol bombs in their possession.

"They have been calling for violence for months," he said. "Our action is against people whose goal is to destroy democratic institutions."