Suspected Islamist militants have killed more than 20 people during attacks on two villages in eastern Congo, the government said on Thursday, the latest in a string of massacres the United Nations has said may constitute war crimes.

The Allied Democratic Forces (ADF), a Ugandan armed group operating in eastern Democratic Republic of Congo for more than three decades, have killed more than 1,000 civilians since the start of 2019, according to U.N. figures.

“They finished off the poor civilians with knives and firearms. People have been panicking since this morning and are already fleeing,” said Rachel Tarwayi, administrator of Irumu territory.

The United Nations says violence attributed to the ADF has soared since the start of the year, following the launch of a large-scale army campaign to wipe out the militia.

As a result, the ADF abandoned its bases, split into smaller more mobile groups, and took revenge on civilians in an attempt to divert the army’s resources to protect villages.

On Wednesday night fighters attacked the villages of Tsabi and Tondoli, around 120 km (74.56 miles) south of the city of Bunia, said Gili Gotabo, head of a civil rights groups in Irumu.

“Among the dead there are unfortunately three village chiefs,” Gotabo said by telephone.

Several attacks attributed to the ADF have also been claimed by Islamic State, although researchers and analysts say there is a lack of hard evidence linking the two groups.

Violence committed by a constellation of more than 100 armed groups has forced over half a million people in the east of the country to flee their homes since the start of the year.

However, the military and security forces have also committed grave violations, including killings and sexual violence, the United Nations has said.