A delay to the start of the talks risks scuppering an ambitious pledge by the two sides to end the fighting in eastern Congo that has killed thousands of people this year and displaced hundreds of thousands more.

M23 rebels seized eastern Congo's largest city Goma in late January as part of a rapid advance that has given them control of more territory than ever before.

U.S. President Donald Trump's administration has mediated talks between Congo and Rwanda that Washington hopes will produce a sustainable peace and attract billions of dollars of Western investment to a region rich in tantalum, gold, cobalt, copper and lithium.

Rwanda, which has long denied helping M23, says its forces act in self-defence against Congo's army and ethnic Hutu militiamen linked to the 1994 Rwandan genocide.

Under a separate but parallel mediation effort hosted by Qatar, Congo and M23 signed a declaration of principles on July 19, opens new tab in which they vowed to start negotiating a peace agreement no later than August 8 with the goal of reaching a deal by August 18.

Bisimwa told Reuters on Thursday, however, that M23 had not received an invitation to Doha and that for now there was no M23 delegation there.

Another rebel leader, speaking on condition of anonymity, told Reuters the group would not go to Doha "until Kinshasa begins to respect the declaration of principles, which provides for the release of our detained members".

An official with knowledge of the matter said there had been a delay in releasing prisoners, but that both sides were still working to implement the terms outlined in the declaration of principles.

"This includes ongoing negotiations to establish a mechanism – with involvement from the International Red Cross – for the exchange of prisoners, which has taken longer than initially anticipated," the official said.

"However, progress is being made, and once there is an agreement on this point, implementation of the deal is expected to pick up pace."

A Congolese government official directly involved in the talks told Reuters that prisoners could only be released after an agreement - rather than the declaration of principles - is signed.

That person said they could not confirm whether Congo would attend the talks.

Tina Salama, spokesperson for Congolese President Felix Tshisekedi, said Congo was still participating in the Doha peace process and would attend any meetings scheduled.

Reporting by Congo newsroom and Maha El Dahan in Dubai, Writing by Portia Crowe; Editing by Robbie Corey-Boulet and Ed Osmond
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