Democratic Republic of Congo President Felix Tshisekedi has vowed “a vigorous and coordinated response” against a rebel alliance that has besieged swaths of the nation’s mineral-rich east and forced hundreds of local troops and foreign mercenaries to surrender.

Congolese President Félix Tshisekedi has vowed to restore government authority in the east, where Rwanda-backed M23 rebels have seized control of the city of Goma and are reportedly advancing south to take more territory.

The weeks-long march of the M23 armed group has prompted calls for crisis talks, as well as rising international criticism and warnings of a looming humanitarian crisis.