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.

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.

Goma, Congo — Residents in eastern Congo’s largest city, Goma, were fleeing on Monday after Rwanda-backed rebels claimed to have captured the regional hub from Congolese forces as fighting escalated despite calls from the U.N. Security Council for the insurgents to withdraw.