Niger President Mohamed Bazoum has termed the death of former Mali Prime Minister Soumeylou Boubèye Maïga an "assassination".

Mr Maïga false died on Monday in custody at a hospital in the Malian capital, Bamako, where he was undergoing treatment.

He had been in detention since last August over corruption allegations.

A court ruled against a plea by Maïga's family for medical evacuation as his health condition reportedly deteriorated.

"[The death of the former Malian Prime Minister] in prison is reminiscent of that of President Modibo Keita in 1977. I thought that such assassinations were from another era," President Bazoum said on Twitter.

The president's reaction could worsen strained relations between the neighbouring countries.

The privately-owned news website Actuniger said President Bazoum "would have done well to limit" his reaction.

Mali's interim leaders sent condolences to Maïga's family in a statement where they hailed the former PM as a "great servant of the state".

Political parties have demanded an inquiry into the death of the former PM who served under the late Ibrahim Boubacar Keita that was ousted by Mali's current military rulers.