The United Nations expressed deep concern at reports of M23 rebels and Rwandan troops advancing south towards the Congolese city of Bukavu on Thursday, as the militants sought also to assert their control over east Congo's largest city Goma.

President of the Democratic Republic of Congo said on Thursday that his troopers are fighting an insurgence by the Rwandan-backed militant group M23 which recently captured swaths of land in the east.

Rwanda-backed rebels claimed on Monday they captured eastern Congo’s strategic city of Goma, the hub of a region containing trillions of dollars in mineral wealth that remains largely untapped.