Congo has severed diplomatic ties with Rwanda as fighting between Rwanda-backed rebels and government forces rages around the key eastern city of Goma.

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

Residents in eastern Congo’s largest city, Goma, woke up on Monday morning afraid and uncertain about who was in control of the area after Rwanda-backed rebels claimed to have captured the city, as their fight with Congolese security forces escalated in recent days in one of Africa’s longest wars.