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.

Congolese forces were losing control of the city of Goma on Wednesday after rebel groups backed by Rwanda took over the airport and shared plans to set up a new administration.

The United States on Tuesday called on the United Nations Security Council to consider measures to stop an offensive by Rwandan troops and M23 rebel forces in eastern Democratic Republic of Congo as a conflict there escalates.