GOMA, Democratic Republic of Congo (Reuters) -Rwandan-backed rebels marched into east Congo's largest city Goma on Monday and troops from the east African neighbours exchanged fire over the border in the worst escalation of the long-running conflict for more than a decade.

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.

Tens of thousands of people are fleeing towns in the Democratic Republic of Congo's east, as rebel forces close in on the city of Goma. Explosions and gunshots were heard in city - home to more than a million people - late on Sunday evening, according to local media reports.

GOMA, Democratic Republic of Congo (Reuters) -Rwandan-backed rebels marched into the centre of east Congo's largest city on Monday, witnesses said, in the latest escalation of decades of conflict in a region already suffering one of the world's worst humanitarian crises.

Rwanda-backed rebels claim they have captured Goma, the largest city in eastern Congo. Congo’s government said the rebel advance was a “declaration of war" and the United Nations has described mass panic among Goma's two million residents.

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.

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.

Rwanda-backed rebels have claimed they captured eastern Congo’s largest city, Goma, as the United Nations describe a “mass panic” among its 2 million people and Congo’s government say the rebel

In the last 48 hours, two U.N. peacekeepers from South Africa and one from Uruguay were killed and 11 peacekeepers were injured and hospitalized.