More than 45 people have been killed and a dozen wounded by a militia group in eastern Congo’s Ituri province, said the United Nations peacekeeping mission in Congo on Monday.

The attack, which occurred Sunday evening into Monday morning, is believed to have been perpetrated by the CODECO militia group, which massacred vulnerable displaced people at the Lala displacement site in Djugu territory, said the U.N.

The peacekeeping mission “extends its condolences to the families of the victims and wishes a speedy recovery to the injured. This attack constitutes a serious violation of international humanitarian law and (the peacekeeping mission) wishes to recall that deliberate attacks against civilian populations can constitute war crimes,” said the statement.

Fighting between CODECO, a loose association of various ethnic Lendu militia groups, and Zaire, a mainly ethnic Hema self-defense group, has been ongoing since 2017 but has worsened recently. Dozens of civilians have been killed by CODECO this year.

In December, the United Nations said the insurgent group was expanding its areas of control, attacking civilians and Congo’s military, and taxing communities in the areas that it holds.

The killings come amid surging violence across eastern Congo, where conflict has been simmering for decades. More than 120 armed groups are fighting in the region, most for land and control of mines with valuable minerals, while some groups are trying to protect their communities.