New York - The US ambassador to the United Nations on Thursday called for a "full investigation" into the death of two UN experts killed in March in the Democratic Republic of Congo.Michael Sharp, a US citizen, and Zaida Catalan, a Swedish-Chilean dual national, were likely murdered by Congolese militia members while on a mission investigating violence and mass graves in the country's restive Kasai province, a UN inquiry out on Wednesday found."The murder of UN experts - especially like Michael and Zaida, who risked their own lives in order to help others - cannot end in a bureaucratic procedure," said US Ambassador Nikki Haley."We still need a full investigation under the Secretary-General's authority into the events surrounding their deaths and accountability for the perpetrators - there is simply no other appropriate course of action," Haley said in a written statement.The statement was released as the UN Security Council began a meeting focused on unrest in the African nation, with DRC Foreign Minister Leonard She Okitundu and relatives of the victims in attendance.Okitundu said that his government does not believe an independent international investigation, as recommended in a UN report, is necessary.He added that nine of 16 identified suspects have been arrested, and that Congolese officials are working with Swedish investigators and US FBI agents."The authors of those crimes will be severely punished," he promised. Calls for a 'full' probe Sharp and Catalan disappeared on March 12. Their bodies were found 16 days later, with Catalan's decapitated. A report sent to the Security Council in June called the murder a "premeditated setup" and that it may have included members of state security services.The report said a group of Congolese, "likely militia members from the Kasai Central province, was responsible," adding that there was "a reasonable likelihood that the killings were committed after consultation with other local tribal actors."The United States expects the DRC "to cooperate with the investigation and get its own house in order by upholding basic human rights, providing security for its citizens, and announcing a timeline for its overdue elections," Haley said.Other Security Council members including France and Sweden also called for a "full investigation" to learn the whole truth, and demanded full cooperation from DRC officials. In less than a year, brutal violence in the five central Kasai provinces has claimed more than 3 000 lives, according to a tally by the Roman Catholic church. Some 1.4 million people have been displaced by the violence.A military tribunal in Kananga has given the go-ahead for all parties to go to the scene of the crime, a visit scheduled for August 21.Haley warned that US officials "will continue to monitor the situation in the DRC carefully and pursue additional Security Council sanctions designations if progress is not made in establishing peace and stability for the Congolese people."