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.'

Congo has severed diplomatic ties with Rwanda as fighting between Rwanda-backed rebels and government forces rages around the key eastern city of Goma.