The United Nations and Congo must investigate after three bodies, including those of Swedish and American investigators with the United Nations, were found in central Congo, Sweden's prime minister said Wednesday.

Stefan Lofven said Sweden was "naturally ready to assist" in investigating the deaths of Swedish national Zaida Catalan, American Michael Sharp and their interpreter Betu Tshintela. Their bodies were found this week in a shallow grave.

They went missing March 12, along with driver Isaac Kabuayi and two motorbike drivers, while looking into large-scale violence and alleged human rights violations by the Congolese army and local militia groups in Central Kasai province.

"After tests … it is possible to identify the bodies as the two UN experts and their interpreter as being found near the Moyo River," said Congo government spokesperson Lambert Mende. Investigations will continue to find other missing Congolese colleagues, he said.

Congo's police Insp. Gen. Charles Bisengimana said the bodies were found Monday between the cities of Tshimbulu and Kananga, the provincial capital.

congo UN investigators dead

Zaida Catalan, of Sweden, left, and Michael Sharp, of the U.S., were the first UN experts reported missing in Congo, according to Human Rights Watch.

The confirmation came a day after Sharp's father, John Sharp of Hesston, Kan., wrote on his Facebook page that the bodies of two Caucasians had been found in shallow graves in the search area for the UN investigators.

"Since no other Caucasians have been reported missing in that region, there is a high probability that these are the bodies of MJ and Zaida," he wrote. "Dental records and DNA samples will be used to confirm the identities. This will take some time.

"All other words fail me."

Sharp and Catalan were "killed senselessly," the U.S. ambassador to the UN, Nikki Haley, said in a statement.

Trying to bring peace

Tuesday night, UN Secretary General Antonio Guterres released a statement offering his "profound condolences" to the families of Sharp and Catalan.

"Michael and Zaida lost their lives seeking to understand the causes of conflict and insecurity in the DRC in order to help bring peace to the country and its people," Guterres said.

He added that the UN hopes further examination will determine their cause of death and the world body will conduct an inquiry into their deaths.

"I urge the Congolese authorities to continue the search for the four Congolese nationals who accompanied our colleagues," he said.

Sharp and Catalan are the first UN experts to have been reported missing in Congo, Human Rights Watch has said, and it is the first recorded disappearance of international workers in the Kasai provinces.

CONGO-POLITICS/PROTESTS

Congo has been wracked by large-scale violence and alleged human rights violations by the Congolese army. An injured supporter of the Congolese main opposition party Union for Democracy and Social Progress (UDPS) is shown being carried away Wednesday following clashes with riot police outside the party headquarters in Kinshasa. (Robert Carrubba/Reuters)

Increasing violence

Parts of Congo, particularly the east, have experienced insecurity for decades, but violence in the Kasai provinces in central Congo represents a new expansion of tensions.

The Kamwina Nsapu militia has been fighting security forces since last year, with the violence increasing after security forces killed the militia's leader in August. More than 400 people have been killed and more than 200,000 displaced since then, according to the UN.

Guterres said that in honour of Sharp and Catalan, the UN will continue to work in Congo.

With files from CBC News