Twenty-four bodies were found at four sites near Oicha in the volatile Beni region, the area’s top administrator Donat Kibwana said.
The Kivu Security Tracker, a joint project of the Congo Research Group and Human Rights Watch put the toll at 19.
DR Congo troops have been carrying out a military operation on the ADF, which originated in Uganda but now active in DRC’s east — long plagued by various militias.
Militiamen have responded with a series of massacres against civilians with gruesome attacks involving machetes.
The ADF, blamed for the deaths of more than a thousand civilians in Beni since October 2014, began as an Islamist-rooted rebel group in Uganda that opposed Ugandan President Yoweri Museveni.
It fell back into eastern DRC in 1995 during the Congo Wars and appears to have halted raids inside Uganda. Its recruits today are people of various nationalities.
UN experts estimated the ADF in 2018 to number around 450 fighters.
A report to the UN Security Council recently said the ADF seemed to follow an extreme Islamist ideology, but there is no information on whether the group has links with international jihadist groups.
The spate of massacres has become a major challenge for President Felix Tshisekedi, who took office a year ago.