Fifteen United Nations peacekeepers were killed in an attack in the Democratic Republic of the Congo on Thursday.
Five Congolese soldiers were also killed in the attack. Over 50 others were injured.
"Elements" of the Allied Democratic Forces, a rebel group, are suspected to have carried out the attack at a base in the North Kivu province. The peacekeepers were there as part of MONUSCO, a U.N. stabilization mission in Congo.
MONUSCO is the U.N.'s largest and most expensive peacekeeping operation. As of October, over 21,000 personnel were deployed in the country. Its budget for the 2017-2018 term is over $1.1 billion.
In March, the Security Council voted to cut the number of troops on the mission. The decision came amid pressure from the U.S. — the largest U.N. donor — to cut costs.
Officials said the Thursday attack is the worst attack against U.N. peacekeepers in recent history.
They think the attack spurred from MONUSCO's "increasingly robust posture" in the region disturbing armed militant groups.