The three-year insurgency by the Rwanda-backed rebel group M23 has intensified, and the U.N. warned the violence could spill into a wider war.

In a statement, the rebels urged residents of Goma to remain calm and for members of the Congolese military to assemble at the central stadium.

Advances being made by the M23 rebel group in the Democratic Republic of Congo are "heightening the threat of a regional war," according to U.N. Secretary General Antonio Guterres.

The M23 militia, funded and directed by Rwanda, said it had seized the city of Goma, terrifying its people, many of whom sought shelter there after fleeing the rebel advance.

M23 rebels said they have advanced into Goma, a large city in the eastern Democratic Republic of Congo. Hundreds of thousands of residents have been displaced.

Rwandan-backed fighters closed in on eastern Congo's largest city of Goma on Sunday (January 26), forcing thousands of civilians to flee and grounding flights from the local airport as government forces battled to stop the rebels seizing the city.

The besieged Congolese city of Goma was rocked by heavy artillery fire on Monday as France warned the regional capital was on the brink of falling to militia fighters and

The Democratic Republic of Congo has severed diplomatic relations with Rwanda. This decision is due to the government in Kigali supporting rebels who are attacking Congolese government forces. At least 13 soldiers from international peacekeeping forces have lost their lives in the internal conflict.