M23 rebels have made rapid advances in the latest bout of conflict that has long-dogged the mineral-rich east.

Advances being made by the M23 rebel group in the Democratic Republic of Congo are "heightening the threat of a regional war," according to U.N. Secretary General Antonio Guterres.

Angolan President Joao Lourenco has urged warring parties in the Democratic Republic of Congo (DRC) to return to peace talks, which collapsed last year, the foreign ministry said.

The violence in eastern Congo has escalated. Near Goma in North Kivu, 13 peacekeepers have been killed by M23 rebels, while Congo has broken off relations with Rwanda. The North Kivu region is rich in gold and coltan.

North Kivu is a province bordering Lake Kivu in the eastern Democratic Republic of the Congo. The capital city is Goma.

M23 rebels claim they now control the Congolese city of Goma—an act Congo's government described as a 'declaration of war.'

The M23 militia, funded and directed by Rwanda, said it had seized the city of Goma, terrifying its people, many of whom sought shelter there after fleeing the rebel advance.

United Nations chief Antonio Guterres on Sunday urged Rwanda to withdraw its forces from the eastern Democratic Republic of Congo where fierce fighting raged as Kigali-backed fighters closed in on the major city of Goma.

Angolan President Joao Lourenco has urged warring parties in the Democratic Republic of Congo (DRC) to return to peace talks, which collapsed last year, the foreign ministry said.

Rwandan-backed rebels moved to tighten their grip on the strategic city of Goma in the east of the Democratic Republic of Congo on Monday in what Kinshasa described as “a declaration of war” by its neighbour.

Located in the Democratic Republic of Congo, it would have twice the power generation of China's Three Gorges and, therefore, be the world's largest hydroelectric plant. The Grand Inga Dam enticed investors and developers but decades after it was first dreamt up,