Niger's coup leaders that toppled Mohamed Bazoum said they would "prosecute" the deposed president for "high treason" and "undermining the security" of the country, in a statement read out on national television.
"The Nigerien government has so far gathered... evidence to prosecute the deposed president and his local and foreign accomplices before the competent national and international bodies for high treason and undermining the internal and external security of Niger," said Colonel-Major Amadou Abdramane.
Earlier on Sunday, head of a religious delegation of mediators said that the leader of military junta is ready to consider a diplomatic solution to the country's stand-off with the West African bloc ECOWAS.
The Economic Community of West African States (ECOWAS) has approved the deployment of a "standby force to restore constitutional order" in Niger as soon as possible but remains committed to finding a diplomatic solution to the crisis.
ECOWAS has not ruled out using force against the army officers who toppled Niger's elected leader Mohamed Bazoum on July 26.
Coup leader General Abdourahamane Tiani "said their doors were open to explore diplomacy and peace in resolving the matter", said Sheikh Bala Lau, a day after his Nigerian Muslim delegation held talks in the capital Niamey.
Tiani "claimed the coup was well intended" and that the plotters "struck to starve off an imminent threat that would have affected" Nigeria as well as Niger, the statement added.
But Tiani said it was "painful" that ECOWAS issued an ultimatum to restore Bazoum without hearing "their side of the matter", according to Lau's statement.
Tiani also apologised for not giving sufficient attention to an ECOWAS delegation to Niger led by former Nigerian leader Abdulsalami Abubakar, saying the treatment was due to anger over the ultimatum.
The Muslim leaders visited Niamey with the blessing of Nigerian President Bola Tinubu, who is also head of ECOWAS.
The bloc scrapped a Saturday crisis meeting on the coup for "technical reasons".
Mohamed Bazoum, 63, and his family have been held at the president's official Niamey residence since last month's coup.