UNITED NATIONS (AP) — The United States and Sweden called Thursday for the United Nations to follow up initial inconclusive investigations into the murder of U.N. experts from their countries in Congo — but Congo says it opposes an independent international inquiry.

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

The two experts disappeared on March 12 while investigating possible violations of U.N. sanctions against Congo and their bodies were discovered in shallow graves on March 27.

U.N. Secretary-General Antonio Guterres said in a letter to the council accompanying the executive summary of the U.N. Board of Inquiry's report that the board called for further investigations and judicial proceedings.

Guterres said he intends to discuss "the establishment of a follow-on mechanism and its mandate" with Congolese officials and council members.

U.S. Ambassador Nikki Haley said the board's report is just the first step "in the pursuit of justice for the horrific murders" and called for "a full investigation under the secretary-general's authority into the events surrounding their deaths."

Sweden's deputy U.N. ambassador Irina Schoulgin-Nyoni noted that a report by Sharp and Catalan's colleagues on the panel of experts monitoring sanctions against Congo recommended continuing investigations.

"We share that view," she said. "No stone should be left unturned in our efforts to deliver justice for those who lost their lives in the service of the U.N." She added that Sweden supports have the secretary-general establish "a mechanism."

Congo's Foreign Minister Leonard She Okitundu noted that the panel of experts recommended establishing "an international independent inquiry" on the murders.

"My government does not think that it's a good idea to establish this kind of inquiry," he told the council.

He said the government is already cooperating with the United Nations, a Human Rights Council inquiry with independent experts, and with U.S. and Swedish authorities.

In addition, Okitundu said the auditor-general of Congo's armed forces has launched an inquiry that has identified 16 suspects. He said nine suspects have been arrested, 19 hearings have been held, and "a visit to the scene of the crime is planned for Aug. 21."

The board of inquiry's executive summary, obtained Wednesday by The Associated Press, said "there was a reasonable likelihood that the killings were committed after consultation with other local tribal actors."

It noted that information is circulating about the possible involvement "of various government individuals or organizations" in the murders but said this isn't proof and additional investigations "may provide greater clarity."

The panel of experts report said Sharp and Catalan "were assassinated in a premeditated set-up" under circumstances that are still unclear.

It said available evidence leaves open the possibility that members of the government's security services, a militia operating in the area, or other armed groups were responsible for their murders.

Ida Sawyer, Central Africa director at Human Rights Watch, said "Guterres should set up a U.N. investigation to uncover the truth." She said that "since Congolese security forces may have been responsible for the killings, the Congolese government cannot be relied on to find the killers."

U.N. spokesman Farhan Haq said Guterres discussed the issue of a follow-on investigation Wednesday with Congo's Okitundu and he is continuing talks with Security Council members.

"We believe that there is progress towards the idea of some form of follow-on mechanism," he told reporters Thursday.