(Reuters) - Residents of eastern Congo's second-largest city on Monday surveyed the aftermath of widespread looting that accompanied the arrival of Rwandan-backed M23 rebels who have pledged to restore order.

The M23 fighters moved into the centre of Bukavu on Sunday, marking the Tutsi-led group's most significant advance since seizing east Congo's biggest city of Goma in late January.

The capture of Bukavu, a commercial hub, and of the strategic airport that services the city in the nearby town of Kavumu dealt a further blow to Kinshasa's authority and escalated a conflict that has fanned fears of an all-out regional war.

Congo's government has so far stopped short of saying Bukavu was fully under M23 control. Congolese and allied Burundian troops withdrew from the city to avoid fighting in densely populated areas, creating a power vacuum that gave rise to looting and a prison break.

In a statement read on local radio on Monday, a rebel alliance that includes M23 said it would assist the population of Bukavu who were "abandoned" by the army and allied combatants.

"Our forces have been working to restore the security for the people and their property, much to the satisfaction of the entire population," it said.

'THEY TOOK EVERYTHING'

Standing before his looted shop, Zozo Sakali said he did not know how he could repay the loan he took out to buy merchandise.

"The thugs arrived, they took everything, and nothing remains. I'm really upset. I don't know how I'm going to repay the money I borrowed," he said.

The well-equipped M23 is the latest in a long line of ethnic Tutsi-led rebel movements to emerge in Congo's volatile east.

Rwanda rejects allegations from Congo, the United Nations, and Western powers that it supports the group with arms and troops. It says it is defending itself against the threat from a Hutu militia, which it says is fighting with the Congolese military.

Congo rejects Rwanda's complaints and says Rwanda has used its proxy militias to loot its minerals.

M23 have now captured more territory than all other rebellions since the end of two major wars that ran from 1996 to 2003. These advances have also handed them control of some of the region's vast and valuable mineral deposits.

Congo is the world's top producer of tantalum and cobalt, a key component in batteries for electric vehicles and mobile phones. It is also the third largest global copper producer and home to significant coltan, lithium, tin, tungsten and gold deposits. The east is rich in tin, tantalum and gold.

(Reporting by Congo Newsroom; Writing by Sofia Christensen; Editing by Robbie Corey-Boulet and Hugh Lawson)