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.

M23 insurgency has intensified, with the Rwanda-backed rebels seizing control of more territory than ever before, prompting the U.N. to warn of the risk of a broader war. South Africa said nine of its peacekeepers were killed in fighting.

Residents of Goma reported gunfire and shelling after rebels overran Congolese troops. U.N. officials estimated that more than 1 million displaced people were now inside the city.

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.

The Democratic Republic of the Congo (DRC) has announced the recall of its embassy staff in Rwanda amid advances by the March 23 Movement (M23) rebellion, which fueled diplomatic tensions between Kinshasa and Kigali.

The M23 armed group and Rwandan soldiers entered the centre of Goma on Sunday night after weeks of advancing on the main city in the Democratic Republic of Congo's North Kivu province.

The M23 rebels announced the capture of Goma in a statement minutes before a 48-hour deadline imposed by the group for the Congolese army to surrender their weapons expired.

The current security crisis in eastern DR Congo, where M23 rebels are closing in on Goma city, "could have been averted" if the government in Kinshasa was committed to peace, Rwanda's Permanent Representative to the United Nations said on Sunday,

In recent weeks, the armed conflict between the M23/AFC and the Congolese army, backed by their allies, has flared up again in the province of North Kivu and spread to the neighbouring province of South Kivu.

The United Nations Security Council convened an emergency meeting to address the escalating violence in the eastern DRC.

M23 rebels claim they now control the Congolese city of Goma—an act Congo's government described as a 'declaration of war.'