Cambodia's U.N.-backed Khmer Rouge tribunal has indicted 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.

An estimated 1.7 million people died due to the communist Khmer Rouge's extremist policies in 1975-79. Two of the group's top leaders received life sentences last August for crimes against humanity.

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.