The Rwandan-backed M23 group on Friday advanced south after seizing the biggest city in mineral-rich eastern DR Congo, in violence that according to the UN has killed at least 700 people in less than a week.

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 Rwanda-backed armed group M23 vowed on Thursday to march on the DR Congo capital, Kinshasa, as its fighters made further advances in the mineral-rich east of the country.