Sweden said it was opening a murder investigation, and the UN Security Council strongly condemned the killings. American Michael Sharp, Swedish national Zaida Catalan and their interpreter Betu Tshintela went missing March 12 along with driver Isaac Kabuayi and two motorbike drivers in Central Kasai province while looking into recent large-scale violence and alleged human rights violations by the Congolese army and local militia groups.
A UN Security Council diplomat, speaking on condition of anonymity because of the sensitivity of the issue, said the experts were investigating alleged mass graves.
It was the first recorded disappearance of international workers in the once-calm Kasai provinces, where the Kamwina Nsapu militia has been fighting security forces since last year.
More than 400 people have been killed and more than 200 000 displaced since government troops killed the militia's leader in August, according to the United Nations.