Two U.N. peacekeepers were killed and several more wounded in an attack Monday in eastern Congo by suspected Ugandan rebels of the ADF group, said a U.N. spokesman.

“One peacekeeper has been killed and 12 injured during an attack of [UN mission] MONUSCO camp at Mamundioma this morning”, said the UN Congo mission spokeswoman Florence Marchal. He said that since last week ADF rebels have resumed attacks on army bases and on civilians. Army spokesman Mak Hazukay said the attacks were carried out simultaneously and hit a United Nations base housing Tanzanian peacekeepers who formed part of an intervention brigade which has a mandate to conduct offensive operations against militants.

According to the UN Spokesperson, the Organization’s Stabilization Mission in the DRC (known by its French acronym, MONUSCO) has deployed attack helicopters as well as the Force Intervention Brigade to support its operations and reinforce its presence.

He urged Congolese authorities to swiftly investigate the incident and bring the attackers to justice.

The Allied Democratic Forces-National Army for the Liberation of Uganda (ADF-NALU) rebel group, which was founded in Uganda in 1995 and later moved to Congo, is believed to have roughly 400 members and has been accused of committing serious human rights violations, including recruiting child soldiers and rape.

The fighting occurred in the territory of Beni, the North-Kivu province near the border with Uganda, which has suffered a wave of violence since 2014 with more than 700 civilians killed, many of them hacked to death.