Assailants attacked the villages of Somakita and Kinsele, in the Kwamouth territory of Mai-Ndombe province, at dawn on Wednesday, according to local civil-society leader Damien Bungu.
Fifteen people were killed in Somakita, he told AFP, while several houses were torched in Kinsele.
Giving a provisional toll, Guy Musomo, a local elected official, said 15 people had been killed while some 200 people had fled the area.
AFP was unable to independently confirm the fatality numbers.
Fighting broke out in Mai-Ndombe in June following a dispute over taxes and land between the Teke and Yaka communities.
Members of the Teke community consider themselves the original inhabitants of villages spread over 200 kilometres (120 miles) along the Congo River. Yeke people settled in the area after the Teke.
Few attacks were recorded in Mai-Ndombe in recent months.
The Democratic Republic of Congo's government has said 180 people have been killed in the conflict. Tens of thousands of people have also fled their villages, according to the United Nations.
Western DRC Bloodied
KIKWIT, DRC - Fifteen people were killed in attacks in western DRC this week, local officials said Thursday, in a flare-up of violence in the region after weeks of calm.
