Dozens of rival militias operate in DR Congo's North and South-Kivu provinces, including the Allied Democratic Forces (ADF), an Islamist-rooted group blamed for killing hundreds.

"Some houses were set on fire in Nyamulongwe village by the militias who were fleeing the army offensive," Gadi Mukiza, a communal leader in South-Kivu, told AFP. "They also stole cattle and escaped."

Nyamulongwe is the seventh village attacked and burned in five days in the South-Kivu's Fizi region, Mukiza said, after Kalonge, Lubemba, Kalongozi, Kyanama, Muganwa and Muburungu, forcing massive displacement of villagers, the official said.

Militias have been launching attacks against army positions for the five days, local military spokesman Captain Dieudonne Kasereka said.

On Tuesday a confrontation also erupted between MaiMai and rival Twigwaneho in a village in Minembwe region, the UN mission MONUSCO said.

Machete- and gun-wielding gangs this week also killed 12 civilians, including two children, in twin overnight attacks in northeast DR Congo, blamed on the ADF militia group.