The Congolese army on Tuesday clashed for a second day with suspected Ugandan rebels blamed for recent massacres in the country's volatile east, civil society and UN sources told AFP.
The battles broke out on Monday when troops attacked rebels who were thought to be organising another possible attack on the town of Beni in the North Kivu province.
A civil society source in the region told AFP that the clashes have killed one army officer and two rebels.
UN's MONUSCO troops were participating in the fighting, a source with the force told AFP on condition of anonymity.
Dozens of people have been killed in recent weeks in attacks blamed on the rebels of the Allied Democratic Forces and National Army for the Liberation of Uganda (ADF-NALU), who have been terrorising the resource-rich region for almost two decades.
The rebels have been hiding out in the Ruwenzori mountains that straddle the border with Uganda since being driven out of the country by President Yoweri Museveni in 1995.
The mainly Muslim rebels have been blamed for atrocities, pillaging villages and forcing locals to fight for them for years, while funding themselves from the lucrative smuggling of wood.
In January, the Congolese army and soldiers of the UN's MONUSCO forces began an offensive against the ADF-NALU, the last major insurgent group active in the region.
Initially, they thought they had severely weakened them, but the rebels have bounced back since the brutal death in August of Congolese army Chief General Jean-Lucien Bahuma.