Cambodia's U.N.-backed Khmer Rouge tribunal has charged another suspect with crimes against humanity, defying for the second time this month a warning from Prime Minister Hun Sen that adding more defendants could cause unrest.

The tribunal announced Friday that the investigating judge filed charges against Aom An, a former Khmer Rouge district commander in central Cambodia. Earlier this month, the judge charged another district commander and the former Khmer Rouge navy chief with homicide and crimes against humanity.

The charges must be accepted by the court's senior judges before the three can face trial.

Some 1.7 million people are estimated to have died in Cambodia due to the extremist policies of the communist Khmer Rouge from 1975 to 1979.