The rebels, which Rwanda denies supporting, have long been funded at least in part by the illicit mineral trade.

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

The United Nations says Rwanda-backed rebels captured large parts of eastern Congo’s largest city of Goma including its airport.

Troops from Democratic Republic of Congo and Rwanda have been firing at each other across their shared border in the eastern Congolese city of Goma, where Rwandan-backed rebels launched an offensive,

Speaking to BBC Newshour while being locked down in a UN bunker in the city, the deputy head of the UN force, Vivian van de Perre, said the M23 rebels had "established" themselves in Goma, but were still facing "pockets of resistance".

The leaders of DR Congo and Rwanda are meeting at an emergency East African summit in Kenya on Wednesday as M23 rebels, backed by Rwandan troops, tighten their grip on the strategic eastern city of Goma.

Kigali’s support of former Democratic Republic of Congo president Joseph Kabila could complicate peace talks, while Goma, the capital of North Kivu Province, is under siege by the M23.

The latest fighting has heightened an already dire humanitarian crisis in the region, forcing half a million people from their homes since the start of the year.

The president of crisis-hit Democratic Republic of Congo was set to meet his Rwandan counterpart at an emergency summit on Wednesday, as fighters backed by Kigali appeared on the brink of seizing the key city of Goma.

Fighting across the largest city in eastern Democratic Republic of Congo and "is still very much ongoing ... it's not over yet," senior U.N. official in Congo, Bruno Lemarquis, said on Monday after Rwandan-backed M23 rebels claimed to have control of Goma.

Residents in eastern Congo’s largest city of Goma are fleeing after Rwanda-backed rebels claimed to have captured the regional hub from Congolese forces.