Rebel forces have been seen in the center of Bukavu, the second largest city in the eastern Democratic Republic of Congo (DRC), on Sunday, residents told CNN, as the fighters push to expand their foothold in the mineral-rich region.

M23 rebels in the Democratic Republic of Congo have captured the eastern city of Bukavu with the backing of Rwandan forces, the second major city in the mineral-rich Kivu region to fall in three weeks.

Burundi is withdrawing its forces from eastern Democratic Republic of Congo where they had been fighting against M23 rebels, four sources said on Tuesday, in a further blow to Congo's army as it struggles to halt a rebel advance.