By Prak Chan Thul
PHNOM PENH (Reuters) - An international judge at a war crimes court in Cambodia charged another former Khmer Rouge cadre with crimes against humanity on Friday, in a further widening of its net of suspects in the tribunal's most sensitive cases yet.
The charges against 79-year-old Ao An, or Ta An, cover alleged "extermination, persecution on political and religious grounds and other inhumane acts" at detention centres under the late Pol Pot's bloody, ultra-Maoist 1970s rule. At least 1.8 million Cambodians died during that time.
Ao An is the third suspect charged this month in cases many investigators and advocacy groups feared might go unheard due to their old age and alleged government attempts to block the proceedings.
The hybrid U.N.-Cambodian tribunal announced the charges for Ao An on Friday in case 004, which includes Im Chaem, a Buddhist nun suspected of running a forced labour camp.
Meas Muth, an 80-something former navy chief who allegedly sent detainees to a torture centre where some 14,000 people died, was recently named in case 003. Another suspect in that case died in 2013.
The decade-old tribunal has delivered guilty verdicts to only three defendants, two of whom - "Brother Number Two" Nuon Chea and former President Khieu Samphan - remain on trial in a separate case.
Case 003 and 004 are strongly opposed by the Cambodian government, police and the national investigating judge, who have been unwilling to cooperate with the tribunal. Experts say high-profile figures in present day Cambodian politics fear they could be implicated in defendants' testimony.
Court spokesman Lars Olsen said Ao An had heard the charges on Friday but had not been arrested.
Cambodian investigating judge You Bunleng issued a statement on Friday saying he regarded Case 003 as completed and he disagreed with the international judge over 004.
Any legal challenge by You Bunleng could further delay a court already criticised for its slow progress.