West African mediators failed to persuade leaders of a military coup in Mali to immediately hand over power to a civilian government during talks on Tuesday, the chairman of the regional bloc said.

Leaders of the 15-member Economic Community of West African States (ECOWAS) met the heads of a junta that on August 18 overthrew President Ibrahim Boubacar Keita, in the bloc's latest attempt to quicken the transition from military leadership.

ECOWAS imposed economic sanctions after the coup, and said a new president should be appointed by Tuesday. Those actions, and multiple diplomatic interventions, appear to have had little effect so far, reinforcing the difficulty regional powers face in shaping events inside the turbulent country.

"We have not reached any agreement with the military junta," said Ghana President Nana Akufo-Addo, the acting ECOWAS chair, after the talks. He said that a mediating mission would return to Mali next week to try to resolve outstanding issues.

"We need a civilian leadership of the transition and we have also made it clear that the minute that leadership input is in place...the sanctions...would be lifted," he said.

Regional leaders fear the coup could set a dangerous precedent in West Africa and undermine a fight in Mali and neighbouring countries in the Sahel region against Islamist militants with links to al Qaeda and Islamic State.

Before the talks began this morning, Akufo-Addo said that the junta leaders needed to hand over power to a transitional government immediately.

But the junta pushed through a charter on Saturday that says the interim president can be a soldier or a civilian and has not yet indicated when the new government would be named. A spokesman for the junta did not respond to a request for comment after the talks.

West African leaders have not said what the consequences would be for failing to meet the deadline. The sanctions include border closures and the suspension of financial flows, though these were eased so they did not hit ordinary civilians.

The leaders said that they would be willing to allow a transitional government to stand for 18 months, longer than the original year it asked for, Akufo-Addo said.