This M23 advance is the gravest escalation in more than a decade of the long-running conflict in eastern Congo, rooted in the spillover of Rwanda's 1994 genocide into Congo and the struggle for control of Congo's vast minerals resources.

Rwanda-backed rebels tightened their grip on Bukavu on Monday, a day after seizing the second major city in eastern Democratic Republic of Congo whose residents appeared resigned to their fate under the new rulers.

M23 rebels in the Democratic Republic of Congo have captured the eastern city of Bukavu with the backing of Rwandan forces, the second major city in the mineral-rich Kivu region to fall in three weeks.