The United States and Sweden are calling for the United Nations to follow up inconclusive investigations into the murder of two U.N. experts from their countries in Congo.

American Michael Sharp and Zaida Catalan, a dual national of Sweden and Chile, were slain in March in Congo's violence-torn Kasai region and their killing was a key issue at a U.N. Security Council meeting Thursday attended by family members who sat in a front row listening intently.

Secretary-General Antonio Guterres said in a letter to the council that he intends to discuss "the establishment of a follow-on mechanism and its mandate" with Congolese official and council members.

U.S. Ambassador Nikki Haley backed a full investigation under Guterres' authority.