Congolese troops have fought back against Rwanda-backed rebels who the U.N. says are moving fast into the South Kivu province after seizing the region’s largest city and an international airport.

(Reuters) -Congolese troops with support from Burundi's army appeared on Friday to be holding back a push south by Rwandan-backed rebels seeking to expand their grip on eastern Congo in a weeks-old advance that has raised fears of a broader regional conflict.

There has been fierce fighting as Rwanda-backed M23 rebels advance towards the second-largest city in eastern Democratic Republic of Congo, marking a further escalation in the region's conflict. M23 fighters have been moving south, towards Bukavu, the capital of South Kivu, after capturing the largest city in the region, Goma.