UNITED NATIONS — Eight U.N. peacekeepers and at least 12 Congolese soldiers were killed in a joint military operation against rebels in Congo's northeast, which is facing a deadly Ebola outbreak, the U.N. Security Council said late Thursday.

U.N. spokesman Stephane Dujarric said 10 peacekeepers also were injured and one was missing after Wednesday's operation that targeted Allied Democratic Forces rebels.

The Security Council's statement said seven of the peacekeepers who were killed were from Malawi and one was from Tanzania.

A U.N. official said U.N. and Congolese forces were attacked while conducting operations to dislodge the rebel fighters from a stronghold in Kididiwe, near the regional capital of Beni. The mission succeeded and a number of rebels were captured, the official said, speaking on condition of anonymity because he was not authorized to discuss the matter publicly.

Congo's volatile east is home to many armed groups vying for control of the mineral-rich region, and the Allied Democratic Forces and Mai-Mai rebel groups are especially active in the Beni area.

The Security Council called on all armed groups to stop the violence immediately and lay down their arms, echoing an earlier statement from U.N. Secretary-General Antonio Guterres' spokesman.

The U.N. chief and the council urged Congolese authorities to apprehend and bring to justice the perpetrators of attacks on civilians, national security forces and U.N. peacekeepers.

The Security Council underlined "that deliberate attacks targeting peacekeepers may constitute war crimes under international law." Council members also stressed that "involvement in planning, directing, sponsoring or conducting attacks" against peacekeepers or U.N. personnel are a basis for sanctions.

Guterres and the council praised the bravery of peacekeepers from Malawi and Tanzania. They said the peacekeepers operate in "an exceptionally difficult environment" to protect local populations against attacks from armed groups.

The Allied Democratic Forces group originated in Uganda as a rebel movement against that country's government and carried out deadly bombings in the 1990s. A military campaign forced them to relocate to eastern Congo.

Since October 2014, the group's fighters have killed more than 1,500 people in the Beni region, where Wednesday's attack took place. U.N. investigators blamed the Allied Democratic Forces for the deadliest single assault on the U.N. peacekeeping mission in Congo in almost 25 years, an attack last Dec. 7 at a base in Semuliki near Beni that killed 15 Tanzanian peacekeepers, wounded 43 others, and left one peacekeeper missing.

In recent attacks, the group has also killed civilians and abducted children in the Beni region.

Rebel attacks have forced suspension of crucial efforts to contain the Ebola outbreak in some areas.

Dr. Peter Salama, the emergencies chief for the World Health Organization, predicted Tuesday that Congo's Ebola outbreak, which has killed more than 200 people, will last at least six more months.

He said makeshift health facilities offering both traditional and modern treatment have become "major drivers" of the current, deadly transmission and are believed to be linked to more than half of the cases in Beni, the largest city affected by the current outbreak.

Salama said the outbreak is "arguably the most difficult context that we've ever encountered," pointing to activities of two armed rebel groups in the region.