A U.N.-backed genocide tribunal has charged a former Khmer Rouge prison chief with crimes against humanity -- the first such indictment against a leader of the regime blamed for the deaths of nearly two million Cambodians.

A statement Tuesday from judges sitting on the domestic and international tribunal said that Kaing Khek Iev, commonly known as "Duch," was placed under provisional detention after being charged.

He was transferred to tribunal headquarters Tuesday from a military prison, where he had been detained since 1999.

Kaing Khek Iev is one of five former Khmer Rouge leaders facing prosecution for their role in the regime's reign of terror from 1975 to 1979. About 1.7 million people died of murder, overwork, and starvation under the Khmer Rouge.

Kaing Khek Iev served as the chief warden at the S-21 prison in Phnom Penh.

About 16,000 people were tortured and interrogated at S-21 for being suspected enemies of the ultra-communist regime. Most were then bludgeoned to death in a field on the outskirts of the capital. Less than 10 prisoners survived.

Some information for this report was provided by AFP, AP and Reuters.