Rwanda-backed rebels claimed they captured eastern Congo’s largest city, Goma, early Monday, as the United Nations described a mass panic among its 2 million people and Congo’s government said the rebel advance was a “declaration of war.

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.

The rebel militia M23, backed by Rwanda, captured Goma, a major city in eastern Democratic Republic of Congo, on January 27, marking a significant escalation in the conflict. M23 had briefly seized the city in 2012 but had been dormant for years.