Congo has severed diplomatic ties with Rwanda as fighting between Rwanda-backed rebels and government forces rages around the key eastern city of Goma, leaving at least 13 peacekeepers and foreign soldiers dead and displacing thousands of civilians.

Rwandan-backed fighters closed in on eastern Congo's largest city of Goma on Sunday, forcing thousands of civilians to flee and grounding flights from the local airport as government forces battled to stop the rebels seizing the city.

Fighting with M23 rebels in eastern Democratic Republic of Congo left six United Nations peacekeepers dead, UN officials said Saturday.