"We are using artillery, indirect fire with mortars and aviation and at the moment we have troops in the front line alongside government forces," said UN force commander General Dos Santos Cruz.
The new UN intervention brigade has a stronger mandate than past peacekeeping missions and is authorised to fight the rebel forces in eastern Congo.
It engaged in fighting for the first time since its creation in March.
Scores of angry residents took to the streets of Goma in protest against the UN intervention following days of violence that have left at least seven dead in the border city.
Two civilians died in the demonstrations and the UN has called for a joint investigation.