The Democratic Republic of Congo and Rwanda have broken off diplomatic ties after an escalation in fighting in eastern Congo near the border with its neighbour.

United Nations chief Antonio Guterres on Sunday urged Rwanda to withdraw its forces from the eastern Democratic Republic of Congo where fierce fighting raged as Kigali-backed fighters closed in on the major city of Goma.

Rebels say they have taken control of the city of Goma in eastern Democratic Republic of Congo, although this has been denied by the government. Residents shared videos of M23 rebels patrolling Goma's main streets following a lightning advance against the Congolese army on Sunday that saw tens of thousands of people fleeing neighbouring towns.

The Democratic Republic of Congo on Sunday called for the United Nations to sanction Rwanda, accusing its neighbour of issuing a "declaration of war" by sending more troops over the

Mount Goma

Gunfire broke out before dawn Monday in the centre of the besieged Congolese city of Goma, after the Democratic Republic of Congo accused neighbouring Rwanda of sending more troops across

Gunfire rang out early on Monday across parts of Goma, the largest city in eastern Congo, hours after Rwanda-backed rebels said they had seized the city despite the United Nations Security Council's calling for an end to the offensive.

A U.N. official says Congolese rebels and allied Rwandan forces have entered the outskirts of Goma and the airport in the key eastern city is no longer in use.

Army spokesman Ronald Rwivanga said "five civilians have died and 25 severely wounded and more were lightly injured" on the outskirts of Rwandan border town Gisenyi.

Residents in eastern Congo’s largest city of Goma are fleeing after Rwanda-backed rebels claimed to have captured the regional hub from Congolese forces.

Heavy gunfire resonated across the key eastern Congolese city of Goma on Sunday from the frontline just a few kilometres away.