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.

The rebels continued advances in eastern Congo despite their own announcement of a cease-fire. The U.N. secretary-general called for them to lay down their guns and agree to mediation.

Rwandan-backed M23 rebels have seized control of the town of Nyabibwe in eastern Democratic Republic of Congo's South Kivu province, eight sources said on Wednesday - an apparent violation of a unilateral ceasefire they declared this week.

Rwandan-backed M23 rebels captured the mining town of Nyabibwe in eastern Congo’s South Kivu province, violating a ceasefire they declared earlier this week, according to NBC News. The rebels now advance toward Bukavu, raising fears of further conflict after seizing the city of Goma last week.

Rwanda-backed rebels who have captured eastern Congo’s largest city say they plan to take their rebellion to the capital and seek to gain political power.