THREE KHMER ROUGE leaders accused of orchestrating Cambodia’s “killing fields” went on trial today in Phnom Penh before a UN-backed tribunal more than three decades after some of the 20th century’s worst atrocities.

The charges against the surviving inner circle of the communist movement include crimes against humanity, genocide, religious persecution, homicide and torture stemming from their 1975-79 reign of terror.

An estimated 1.7 million people died of execution, starvation, exhaustion or lack of medical care as a result of the Khmer Rouge’s radical policies.

Intellectuals, entrepreneurs and anyone considered a threat were imprisoned, tortured and often executed.

The defendants are 85-year-old Nuon Chea, the Khmer Rouge’s chief ideologist and the No 2 leader behind the late Pol Pot; 80-year-old Khieu Samphan, an ex-head of state; and 86-year-old Ieng Sary, the former foreign minister.

A fourth defendant, 79-year-old Ieng Thirith, was ruled unfit to stand trial last week because she has Alzheimer’s disease.

She is Ieng Sary’s wife and served as the regime’s minister for social affairs.

The Khmer Rouge’s supreme leader, Pol Pot, died in 1998 in Cambodia’s jungles while a prisoner of his own comrades, who after being toppled from power fought a guerrilla war that did not fully end until the late 1990s.

There is serious concern that justice may not be done if any of the aging and infirm defendants dies before a trial is finished.

In September, the tribunal announced it would split up the indictments according to charge into separate trials in order to expedite the proceedings.

The current trial is considering charges involving the forced movement of people and crimes against humanity.

Chea Leang, Cambodian co-prosecutor, recalled for the court the brutalities of Khmer Rouge rule, beginning on April 17, 1975, when they captured Phnom Penh to end a bitter five-year civil war, and immediately began the forced evacuation to the countryside of the estimated 1 million people who had sheltering in the capital.

She also recounted the new social order established by the group: Personal property was banned, religion, press and all personal freedoms abolished.

Pol Pot had led the Khmer Rouge from its clandestine revolutionary origins to open resistance after a 1970 coup installed a pro-American government and dragged Cambodia directly into the maelstrom of the Vietnam War.

When the Khmer Rouge took power in 1975, they all but sealed off the country to the outside world.

Economic and social disaster ensued, but the failures only fed the group’s paranoia, and suspected traitors said to be working with the US, or Vietnam, the country’s traditional enemy, were hunted down.

Vietnam sponsored a resistance movement and invaded, ousting the Khmer Rouge from power in 1979 and installing a client regime.

The tribunal, which was established in 2006, has tried just one case, convicting Kaing Guek Eav, the former head of the regime’s notorious S-21 prison, last July and sentencing him to 35 years in prison for war crimes, crimes against humanity and other offences.

Those going on trial Monday have steadfastly maintained their innocence.