Peace talks between Congo's government and Rwanda-backed M23 rebels planned for Wednesday in Doha have been postponed, sources from both sides told Reuters this week, with no future date set.

The parties had earlier this month billed the meeting as the first direct talks since M23 fighters captured eastern Congo's two largest cities. The rapid offensive has left thousands dead, forced hundreds of thousands more from their homes and raised fears of a wider regional conflict.

It was unclear why the meeting was delayed. Both sides said invitations had not been sent as of Monday. "It's simply a matter of organisation," a Congolese official said.

Last month, Qatar brokered a surprise sit-down between Congolese President Felix Tshisekedi and Rwandan President Paul Kagame during which the two leaders called for a ceasefire.

The United Nations and Western governments say Rwanda has provided arms and troops to the ethnic Tutsi-led M23. Rwanda has denied backing M23 and says its military has acted in self-defence against Congo's army and a militia founded by perpetrators of the 1994 genocide.

The conflict is rooted in the long fallout from the 1994 genocide in Rwanda and competition for control of mineral riches. The armies of Congo, Rwanda and Burundi have all participated in the fighting, raising fears of an all-out regional war.

M23 had long demanded direct negotiations with Kinshasa, but Tshisekedi had refused, arguing that M23 was merely a front for Rwanda.

A source with knowledge of the talks in Qatar told Reuters on Saturday that representatives of Congo's government and M23 held a "discreet meeting" in Doha last week, "marking their first direct encounter in a long time."

The source said that meeting helped spur the rebels to withdraw from the strategic mining town of Walikale. Washington has also pushed both sides to withdraw from the area so mining operations nearby can resume.