BENI, DR Congo: At least 15 civilians were massacred overnight in eastern DR Congo, a monitoring group in the region said Monday, saying the notorious ADF militia were suspected.

The Allied Democratic Forces is a historically Ugandan Islamist group that has holed up in eastern Democratic Republic of Congo since 1995.

It has the reputation of being the bloodiest of the 122 militias which plague the eastern DRC, many of them a legacy of the Congo Wars of the 1990s.

"At least 15 civilians were killed last night in Bulongo (Beni territory, North Kivu). The ADF are suspects," the Kivu Security Tracker (KST) group posted on Twitter.

Local sources separately confirmed the attack and also blamed the ADF.

Kasali bin Kapepela, head of an association of local NGOs, said an "ADF raid' occurred around midnight.

Twelve bodies were found, at least four of whom were women, and some had been beheaded, he said.

Local people gathered to protest the attack. One young man was killed by a stray round and another was seriously injured when police opened fire to disperse the crowd, Jean-Paul Muhindo Katembo, a senior local administrator, told AFP

A source at the UN peacekeeping mission in the DRC, MONUSCO, said the attack occurred around 2am in the Mutilipi district of Bulongo, and that the force had sent a rapid intervention unit in response.

The ADF has killed at least 1,219 civilians in the Beni area since 2017, according to the KST.

The massacres have become more frequent since the DRC's armed forces launched an offensive in October 2019, forcing the ADF to break up into smaller, highly mobile units, say experts.