Nearly three thousand people have been killed in the city of Goma in the eastern Democratic Republic of Congo, according to the United Nations, after the provincial capital was captured by rebels following days of fierce fighting with the Congolese army.

When M23 rebels swept into the Congolese city of Goma this week, world powers urged them to immediately withdraw. Instead, the Rwanda-backed insurgents are intent on showing they can restore order and govern.

The rebels said the ceasefire would start Tuesday. The announcement came shortly after the U.N. said 900 people were killed in last week’s fighting in Goma between rebels and Congolese forces.