PHNOM PENH, Cambodia - Cambodia's UN-backed Khmer Rouge tribunal has charged two more suspects, risking a confrontation with the country's prime minister, who has warned against adding new defendants.

The tribunal announced Tuesday that former Khmer Rouge navy chief Meas Muth and former district commander Im Chaem have been charged in absentia with homicide and crimes against humanity, including enslavement and persecution on political and ethnic grounds.

The charges must be accepted by the court's senior judges before the two are indicted to face trial.

Some 1.7 million people are estimated to have died from starvation, disease and execution due to the extremist policies of the Khmer Rouge from 1975 to 1979. Khieu Samphan, the regime's head of state, and Nuon Chea, right-hand man to the communist group's late leader, Pol Pot, received life sentences last August after being found guilty of crimes against humanity. Their trial on additional charges is ongoing.

Prime Minister Hun Sen said in a speech last week that if the tribunal targeted more defendants, it could incite former Khmer Rouge members to start a civil war.

The Cambodia Daily reported that Hun Sen, speaking at an event marking the UN's “Responsibility to Protect” anti-genocide initiative, said the court's investigations had “almost gone beyond the limit” and could cause former Khmer Rouge soldiers to return to the jungle to fight.

“The value of peace and the cost of human lives have to be considered,” he was quoted as saying.

Hun Sen, who rules Cambodia with an iron hand, has issued such warnings before, even though the Khmer Rouge were already a spent force almost two decades ago.

Hun Sen himself was a mid-level commander with the Khmer Rouge before defecting while the group was still in power, and several senior members of his Cambodian People's Party share a similar background. He helped cement his political control by making alliances with other former Khmer Rouge commanders.

“The decision to charge Meas Muth and Im Chaem offers an important step forward in the much-delayed pursuit of justice for the victims of the atrocities covered in these two cases,” said James A. Goldston, executive director of the Open Society Justice Initiative, an independent organization that has been monitoring the trials.

“The Cambodian government signed an agreement that requires it to support this prosecution; we urge them, and the international community, to stand by that commitment,” he said in an emailed statement.

Tuesday's charges were brought by the international co-investigating judge of the tribunal, which follows the same French-style legal procedures as Cambodian law. The tribunal operates under a unique system pairing international and Cambodian judges and lawyers. Critics claim that the Cambodian jurists are susceptible to political pressure, but the tribunal is structured to make it difficult for either partner to exercise a veto over proceedings.

Some of the charges against Meas Muth involve accusations of torture and killing of Vietnamese, Thais and other foreigners captured at sea or on disputed island territory. Im Chaem headed a Khmer Rouge security centre in the northwest where an estimated 40,000 people died.

Both suspects had been advised in 2012 that they were officially under investigation and should seek legal counsel. Ang Udom, a lawyer for Meas Muth, said his client is in Cambodia and will not flee. Im Chaem, who lives in a former rural stronghold of the Khmer Rouge, has been quoted in interviews as saying she does not recognize the court's authority.

Tribunal spokesman Lars Olsen said the two were charged in absentia to expedite the legal process, as it had not been possible to get arrest warrants executed within a reasonable time.

“Decisions on whether these cases will end up with indictments or dismissals are expected next year, and the charged persons are presumed innocent until proven guilty through a final judgment,” he said in an email.