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.

Congo has severed diplomatic ties with Rwanda as fighting between Rwanda-backed rebels and government forces rages around the key eastern city of Goma, leaving at least 13 peacekeepers and foreign soldiers dead and displacing thousands of civilians.

Rwandan-backed rebels have taken over much of the city of Goma in the east of the Democratic Republic of Congo, although some gunfire can still be heard. There are reports of Congolese and Rwandan troops firing at each other across the border. Columns of M23 rebels have entered the city.

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.

Footage shows troops, some in army uniform, handing over arms to Rwandan security officers after crossing into eastern neighboring country at the main border crossing in Rwanda's Rubavu district - Ana

Rebels claim to have captured the key city of Goma in the DRC, as the decades-long conflict becomes even more volatile. Sky News takes a look at what's going on.

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.

Congolese M23 rebels entered the centre of the eastern city of Goma on Monday, two witnesses said, hours after they claimed to have seized the city despite the United Nations Security Council demanding an end to the offensive.

In the aftermath of its withdrawal from Goma, the M23 suffered a series of heavy defeats at the hands of the Congolese army, which was backed by a multinational force. The M23 were subsequently expelled from the country. M23 fighters then agreed to be re-integrated into the army in return for promises that Tutsis would be protected.

M23 fighters have been pressing to capture strategic eastern city for months and intensified offensives in recent days.

The United Nations Security Council on Sunday demanded that M23 rebel forces stop an ongoing offensive and advance towards Goma, the largest city in eastern Democratic Republic of Congo, and that "external forces" in the region immediately withdraw.