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.'

STORY: Rwandan-backed rebels marched into eastern Democratic Republic of Congo's largest city on Monday, according to witnesses.That's prompted thousands of people, including Congolese soldiers, to flee across the border into Rwanda.