(Reuters) -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.

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

Thirteen soldiers serving with peacekeeping forces in the Democratic Republic of Congo have been killed in clashes with rebels from the M23 group. The South African military said nine of its soldiers died helping to push back a rebel advance on the city of Goma,