Bazoum who has been held in the basement of his palace since the military staged a palace coup about three weeks ago, is said to be in “good spirits” despite being held in “difficult” conditions.

The junta said in a statement on state television said it had gathered evidence to prosecute “the deposed President as well as his local and foreign accomplices for high treason and undermining the internal and external security of Niger”. It did not give further details.

Bazoum, 63, is being held captive with his wife and son and there were growing concerns about their health.

The head of the presidential guards, Gen Abdourahmane Tchiani, declared himself Niger’s new ruler on July 26, and since then the Economic Community of the West African States (ECOWAS) has imposed economic sanctions on the country and threatened military action to reverse the coup.

The coup leaders have warned they will defend themselves against any intervention.

On  Saturday, a high-powered delegation of Muslim clerics from neighbouring Nigeria met junta leaders in Niamey in a bid to mediate an end to the crisis.