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.

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.

Residents of Goma reported gunfire and shelling after rebels overran Congolese troops. U.N. officials estimated that more than 1 million displaced people were now inside the city.