The capture of Bukavu would represent an unprecedented expansion of territory under the M23's control since the latest insurgency started in 2022.

"The fighting that is raging in South Kivu — as a result of the continuation of the M23 offensive — threatens to push the entire region over the precipice," Guterres said without mentioning Rwanda. "And the sovereignty and territorial integrity of the DRC must be respected," Guterres added.

M23 rebels in the Democratic Republic of Congo have captured the eastern city of Bukavu with the backing of Rwandan forces, the second major city in the mineral-rich Kivu region to fall in three weeks.