Maiga was a close ally of former president Ibrahim Boubacar Keita, who was overthrown by strongman Colonel Assimi Goita in a military coup in August 2020.

The former prime minister had been in custody since August 2021, under indictment for fraud among other charges, before being transferred to the clinic where he died this week, aged 67.

Late Monday, a group of political parties named the "Cadre d'echange", or Exchange Framework, stated that Maiga had died "a political prisoner, in very troubling conditions".

The group of about a dozen parties -- of which Maiga was a leader -- called on Mali's army-dominated government to establish an independent inquiry into his death.

Another political group, Parena, also urged the authorities to investigate Maiga's death on Monday.

The former prime minister's relatives had requested his release arguing he needed urgent medical treatment, but the had authorities refused.

His brother Tiegoum Boubeye Maiga likened the death to a "planned assassination".

"Either they wanted to kill him, or make him impotent for life," he said.

Maiga was appointed Keita's prime minister in 2017 but resigned in April 2019 over a massacre that left 160 people dead.

Mali has been struggling to contain a jihadist insurgency that broke out in 2012 and spread from the north to the centre, neighbouring Burkina Faso and Niger.

Thousands of people have been killed and hundreds of thousands been displaced in the conflict, crippling an already impoverished country.

Army officers led by Goita deposed Keita after weeks of protests over his failure to defeat the jihadists and anger over perceived government corruption.