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.

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.

The Eastern Congo rebel alliance that includes the M23 has declared a ceasefire for humanitarian reasons starting on Feb. 4, the group known as the Congo River Alliance said in a statement.