At least 22 civilians were killed by extremist rebels in eastern Congo - the group's second large-scale deadly attack of the week, local authorities said Saturday.

Fighters with the Allied Democratic Forces — which has ties to the Islamic State group — attacked people in Beni territory in North Kivu province late Friday evening, said Nicolas Kambale, the mayor of Oicha commune where the attacks occurred.

“The enemy killed them savagely and as we speak we have at least 22 civilians killed who are already in the morgue,” Kambale said Saturday.

Violence has been simmering in eastern Congo for decades where some 120 armed groups have been fighting over land, resources, power and some to defend their communities. Attacks by rebel groups like ADF have increased recently. Since April last year, ADF attacks have killed at least 370 civilians and abducted several hundred more, including a significant number of children, according to the United Nations.

The group, which originally operated in North Kivu province, has spread to neighboring Ituri province, where more than 144,000 people have been displaced between January and February, according to the U.N. Efforts by Congo’s army and Ugandan forces to push them back have yielded little results.

Friday's attack came days after ADF killed more than 30 civilians, including women and children, between the Irumu and Mambasa territories in Ituri.

A spokesman for Congo's army in Beni, Capt. Antony Mwalushayi, said the attack Friday was in retaliation for large-scale offensives that the military has been conducting in the area.