Nearly 3,000 people have been killed in the city of Goma in the eastern Democratic Republic of Congo, according to the United Nations, after it was captured by rebels following days of fierce fighting with the Congolese army.

Rwandan-backed rebels are gaining ground in eastern Congo despite the unilateral ceasefire they declared earlier this week

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.