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.

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 of Goma reported gunfire and shelling after rebels overran Congolese troops. U.N. officials estimated that more than 1 million displaced people were now inside the city.