Congo’s government has described the unilateral ceasefire declared by Rwanda-backed rebels in eastern Congo as “false communication,” while the United Nations on Tuesday noted reports of heavy fighting with Congolese forces in the region.

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.