Rwandan-backed rebels marched into east Congo's largest city Goma on Monday and Congolese troops exchanged fire with the Rwandan military across the border, in the worst escalation of a long-running conflict for more than a decade.

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

Fighting between M23 and Democratic Republic of the Congo forces has displaced 400,000 since the start of this year, according to the United Nations