Rwanda-backed rebels who have captured eastern Congo’s largest city say they plan to take their rebellion to the capital and seek to gain political power.

Rwanda-backed M23 rebels are moving “rapidly” through South Kivu province toward the city of Bukavu in eastern Democratic Republic of Congo, the United Nations said.

The United Nations expressed deep concern at reports of M23 rebels and Rwandan troops advancing south towards the Congolese city of Bukavu on Thursday, as the militants sought also to assert their control over east Congo's largest city Goma.