Mali's ousted interim president and prime minister have been freed after they were detained by the military and later resigned, an aide to the vice-president said on Thursday.

Interim president Bah Ndaw and Prime Minister Moctar Ouane were arrested and taken to a military base outside the capital on Monday, triggering a crisis in the West African country and drawing threats of sanctions from major powers.

The two men resigned from their posts while in detention on Wednesday.

The arrests, orchestrated by Vice President Assimi Goita, have jeopardised Mali's transition back to democracy after a coup in August overthrew former President Ibrahim Boubacar Keita.

Goita, a colonel, also led last year's coup. He has promised that elections planned for next year will go ahead.

“They resigned, their release was scheduled, we have nothing against them,” said Goita aide Baba Cissé.

Ndaw and Ouane's whereabouts will be kept secret to protect their security, Cissé told Reuters. He declined to detail any plans for their replacement.

Goita ordered their arrest after a cabinet reshuffle in which two fellow coup leaders were sacked from their posts.

Their resignations coincided with a visit by an Economic Community of West African States delegation to press the military to back down. ECOWAS has floated the possibility of sanctions against the officers responsible for the takeover.

Mali's influential M5-RFP political coalition, which led antigovernment protests ahead of last year's coup, has opposed the leadership of Ndaw and Ouane, but it said it would strongly oppose Goita's appointment as president.

Though considered by analysts to be Goita's most likely future governing partner, the coalition said talks with ECOWAS had failed in part because of him.

ECOWAS did not comment about the talks on Thursday.

“The discussions yesterday were unsuccessful because Assimi wants to be the president, which is contrary to the texts of the Transition Charter,” Nouhoum Togo, a spokesperson for M5-RFP, told Reuters.

“Nowhere is it stipulated that the vice-president can replace the president,” he said.