"I saw four civilians killed by bullets... And seven patients and a nurse cut up by machete at the hospital," a regional official told AFP at Eringeti in the north of the troubled North Kivu province.
A local non-governmental organisation however put the toll much higher, at 30 dead: 14 rebels, seven civilians, eight Congolese soldiers and one soldier with the large UN mission in the DRC, MONUSCO.
The Study Centre for the Promotion of Peace, Democracy and Human Rights (CEPADHO) blamed the attack on Ugandan rebels of the Allied Democratic Forces (ADF), who have moved beyond bases in the Ruwenzori mountains by the Ugandan border.
The rebels "attacked our positions at Eringeti and we repelled them all night," said a Congolese army spokesman in the region, Lieutenant Mak Hazukay, declining to give any figures.
Also Read
The mostly Muslim rebels, who have been active in the forested region since being driven out of their homeland in 1995, are accused of a series of killings which have claimed the lives of more than 450 civilians since October 2014.
ADF leader Jamil Mukulu was arrested in Tanzania in April and extradited to Uganda in July.
The ADF, which first emerged in Uganda with the aim of toppling President Yoweri Museveni and setting up a hardline Islamist state, is accused of numerous serious violations of human rights.
The rebels also engage in a profitable illegal traffic in prized tropical timber.
MONUSCO -- the United Nations Stabilisation Mission in the Congo (MONUSCO) -- comprises about 20,000 uniformed personnel overseeing the disarmament, demobilisation, repatriation and reintegration programme for rebel groups.