KINSHASA (Reuters) - A military prosecutor in Democratic Republic of Congo said on Saturday that two men would soon face trial for the murder of two U.N. investigators and denied that Congolese forces were implicated in the crime.

U.N. investigators Michael Sharp, an American, and Zaida Catalan, a Swede, were killed in March in central Congo’s Kasai region, where hundreds have died since last July in an insurrection against the government.

Military prosecutor Colonel Odon Makutu told reporters in the capital Kinshasa that the two suspects, Gerard Kabongo and a local chief named Mulumba Muteba, have been charged with the war crimes of murder and mutilation as well as terrorism and participation in and command of an insurrectional movement.

“As for the killings of the two U.N. experts, two insurgents are in custody out of 16,” Makutu said.

Insecurity in Congo, where millions died in civil wars around the turn of the century, has worsened since December when President Joseph Kabila refused to step down at the end of his constitutional mandate.

Rights group say they suspect Congolese forces could have been involved in the murders of the investigators who report to the U.N. Security Council on human rights abuses and sanctions violations.

“Given the implication of Congolese army soldiers in much of the violence ... we have serious doubts about the Congolese authorities’ ability or willingness to carry out a credible, independent investigation,” Ida Sawyer, Human Rights Watch’s Central Africa director, told Reuters.

The United Nations has repeatedly accused Congolese troops of using excessive force in the conflict and has found 42 mass grave sites it says may need to be probed by the International Criminal Court if the government fails to.

The government has denied it uses excessive force and Makutu said there was no evidence Congolese forces were involved in the investigators’ deaths.

“For the murders of the expatriates, no agent of the security forces has been implicated,” he said.

Last month, the government screened a video for journalists showing Sharp and Catalan’s executions by men wearing red headbands characteristic of the local Kamuina Nsapu militia to rebuff suggestions authorities were complicit in the killings.

But many analysts say the grainy and highly-edited video raises more questions than it answers, including why the assassins from the Tshiluba-speaking militia gave orders in Lingala, the language of western Congo and the army.

A U.N. board of inquiry is investigating the experts’ murder but is not expected to assign blame. Sweden has also opened a police investigation.

The investigators’ interpreter and three moto taxi drivers who went missing with them have not been found, Makutu said.