Local sources said Kigali-backed fighters were advancing on a new front and had seized two districts in South Kivu province, after the rebel group’s capture of most of Goma, the capital of North Kivu.

Rwanda's ally Uganda, unhappy about another rebel group in DR Congo that threatens its security, has also been accused of helping the M23 - with its officers also spotted at Tchanzu. The UN experts say Uganda has also supplied weapons, hosted rebel leaders and allowed cross-border movements of M23 fighters - accusations Kampala denies.

The group's capture of most of Goma, the capital of North Kivu province, is a dramatic escalation in a region that has seen decades of conflict involving multiple armed groups.