Angola will step down from its position as a mediator between parties involved in an escalating Rwanda-backed rebel offensive in eastern Congo, the presidency said on Monday, with another African state set to lead efforts to get peace talks back on track.

The ethnic Tutsi-led M23 escalated their long-standing rebellion this year, seizing east Congo's two biggest cities since January and encroaching into territory rich in minerals such as gold and tantalum.

As the current rotating African Union (AU) Chairperson, Angola's President Joao Lourenco had been trying to mediate a lasting ceasefire and lower tensions between Congo and neighbouring Rwanda, which has been accused of backing M23. Rwanda denies this.

Congo and M23 were scheduled to hold direct talks for the first time in Angola's capital Luanda last week after Congo's President Felix Tshisekedi, who had long refused dialogue with the rebels, agreed to send a delegation.

M23 pulled out at the last minute, following European Union sanctions against M23 and Rwandan officials.

"Angola considers the need to free itself from the responsibility of the mediator of this conflict" to "devote itself more" to the AU's overall priorities, the presidency said in a statement that mentioned the "aborted" meeting in Luanda.

Another head of state will be appointed to the task in coming days, the statement said.

There have been several attempts to resolve the conflict, rooted in the fallout from Rwanda's 1994 genocide and competition for mineral riches, including several ceasefires that were violated, international condemnations, sanctions and regional summits.

The regional blocs of southern and eastern Africa will hold a second joint summit on Monday to address the crisis. Kenya's President William Ruto and his Zimbabwean counterpart Emmerson Mnangagwa will co-chair the virtual event.

M23 last week dismissed a joint call for an immediate ceasefire by Congo and Rwanda and reiterated demands for direct talks with Kinshasa, saying it was the only way to resolve the conflict.

The rebel group said over the weekend that it would withdraw forces from the seized town of Walikale in support of peace efforts.

In response, Congo's army said it would observe the announced withdrawal and refrain from any offensives against enemy forces to encourage de-escalation.

A civil society source and a resident in Walikale said on Monday that M23 were still in the town.