A conflict that has raged for decades reached a flashpoint this week when rebels backed by Rwanda marched on a key Congolese city in a bid to occupy territory and exploit minerals.

After a lightning offensive, M23 rebels now control Goma, a large city in the eastern Democratic Republic of Congo.

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.