Around 30 people were killed Saturday morning in attacks in South Kivu, east of Democratic Republic of Congo (DR Congo), a local official said, Xinhua reported.
The victims, including women and children, were shot, stabbed or burned in houses, according to the official on condition of anonymity.
He said the attacks were caused by a dispute over cows and people from diverse tribes were involved in the conflict.
Some local media blamed the attacks on rebels from Burundi's National Liberation Forces (FNL).
South Kivu is a mountainous region where more than 100,000 people are still affected by activities of militia groups. Several attacks were reported last month that civilians and militia fighters died.
DR Congo's national army had launched offensives against rebel positions since last year.