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.

A rebel group that claimed to have captured the city of Goma in the eastern Democratic Republic of Congo last week has called for an immediate humanitarian ceasefire, after fighting with the Congolese military has left hundreds of people dead.

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.