The conflict between Teke and Yaka communities that started in 2022 over a land dispute caused a deterioration in the humanitarian and security situation in several provinces near the capital Kinshasa.
At least 3,000 people have been killed and more than 150,000 displaced by the conflict, according to the United Nations.
The clashes in Mai-Ndombe province killed 10 Mobondo militants, allied with the Yaka community, and one soldier, village chief Stany Libie and civil society leader Martin Suta told Reuters.
Both accused the government of failing to put an end to the conflict.
"People are dying, villages are emptying, soldiers are falling, and we wonder why the government has been unable to take effective measures to resolve this problem once and for all for the past two years," Libie said.
Congo's army did not immediately respond to Reuters requests for comment.
(Reporting by Ange Kasongo; Additional reporting by Sonia Rolley; Writing by Anait Miridzhanian and Portia Crowe; Editing by David Gregorio)
