The communist movement's chief ideologist did not directly respond to the horrors that prosecutors described a day earlier at the start of the U.N.-backed tribunal for him and two other top Khmer Rouge leaders.

Instead, Nuon Chea gave a political history of the movement and Cambodia, insisted his role was patriotic, and blamed neighboring Vietnam for much of the country's troubles.

``I had to leave my family behind to liberate my motherland from colonialism and aggression and oppression by the thieves who wish to steal our land and wipe Cambodia off the face of the Earth,'' Nuon Chea said in his first public comments at the trial.

``We wanted to free Cambodia from being a servant of other countries, and we wanted to build Cambodia as a society that is clean and independent, without any killing of people or genocide,'' he said.

The tribunal is seeking justice on behalf of the 1.7 million people _ as much as a quarter of Cambodia's then-population _ estimated to have died from executions, starvation, disease and overwork when the Khmer Rouge held power in 1975-79.

The three most senior surviving leaders _ Nuon Chea, 85; former head of state Khieu Samphan, 80; and former Foreign Minister Ieng Sary, 86 _ are charged with crimes against humanity, genocide, religious persecution, homicide and torture. They have long denied blame.

Nuon Chea was the Khmer Rouge's second-highest leader after Pol Pot, who died in 1998 in a jungle while a prisoner of his own comrades. Prosecutors earlier Tuesday said the defendants cannot blame Pol Pot alone for the atrocities that took place.

Prosecutor Andrew Cayley said that like Pol Pot, the defendants exercised life-and-death authority over Cambodia while in power.

``The accused cannot credibly claim they did not know and had no control over the crimes that occurred,'' he said.

Prosecutors have described a litany of horrors, large and small, saying the Khmer Rouge sought to crush not just all its enemies, but seemingly, the human spirit.

Khmer Rouge rule began April 17, 1975, when it captured Phnom Penh to end a bitter five-year civil war and immediately forced the evacuation of the capital, where 1 million people had sheltered. The country was almost sealed from the outside world and most people were forced to work on giant rural communes as the Khmer Rouge attempted to create a pure agrarian socialist society.

People were deprived of any private life, and forced marriages took the place of love. Intellectuals, entrepreneurs and anyone considered a threat were imprisoned, tortured and often executed in so-called ``killing fields.''

Economic and social disaster ensued, but the failures only fed the group's paranoia, and suspected traitors were hunted down, only plunging the country further into chaos.

Vietnam, whose border suffered bloody attacks by Khmer Rouge soldiers, sponsored a resistance movement and invaded, ousting the Khmer Rouge in 1979 and installing a client regime.

Nuon Chea did little to directly address the allegations of atrocities when he spoke for about an hour and a half Tuesday in time allotted for defense rebuttals of the prosecutors' statements.

He told the tribunal he has waited a long time to explain ``a proper history'' of Cambodia to its people and thanked Cambodian heroes who devoted their life to defending the country.

Nuon Chea's co-defendants were very much the public face of the Khmer Rouge as they sought diplomatic support after being ousted. He was more secretive but became more familiar last year with the release of a documentary, ``Enemies of the People.''

I have always said I made mistakes. I am regretful and I have remorse. I am sorry for our regime. I am sorry,'' Nuon Chea told Cambodian filmmaker Thet Sambath.

But he was clear the Khmer Rouge leaders had seen their primary duty as safeguarding the revolution and said suspected traitors were killed because they ``were enemies of the people.''

In court Tuesday, Nuon Chea reiterated the Khmer Rouge's longstanding position that concern about Vietnamese intentions contributed to the Khmer Rouge's decision to forcibly evacuate Phnom Penh in 1975.

The capital's evacuation is expected to be a focus of the current trial, as the tribunal grouped similar charges together to speed the process. Allegations involving the forced movement of people and crimes against humanity are being handled now, with genocide, torture and other charges being decided later.

Even streamlined, the proceedings are likely to be lengthy. After prosecution and defense statements, actual testimony is to begin Dec. 5.

``Here in Cambodia, a unique opportunity has been given ... to set a powerful example, and to send a strong warning from the past to the future so that human beings everywhere can rightfully expect to live in peace under the law,'' Cayley said.

The defendants are old and infirm, and there are fears they won't live long enough for justice to be achieved. A fourth defendant, the Khmer Rouge's social affairs minister, was ruled unfit to stand trial because of Alzheimer's disease.

Judge Nil Nonn denied a second request Tuesday for defendant Ieng Sary to follow the proceedings from another room to ease his physical burden. The judge said it was important for all the defendants to be present for the prosecution's statement.

Some of those attending the trial have provided their own vignettes of the terror: a commune chief who said he killed others because otherwise he would have been killed himself; a man who lost four siblings and law school and police academy students born long after the regime ended.

Two-thirds of Cambodians today were not yet born when the communist group's reign of terror ended in 1979.

The tribunal, which was established in 2006, has tried just one case, convicting former prison chief Kaing Guek Eav for war crimes, crimes against humanity and other offenses. His sentence was reduced to 19 years due to time served and other technicalities.

That case is seen as much simpler than the broader current case against three higher-ranked regime leaders. Kaing Guek Eav confessed and was implicated by meticulously kept prison records.

The case has been overshadowed in the past year by claims that political interference would keep the tribunal from pursuing more suspects. Prime Minister Hun Sen has publicly declared he is against further trials, which he claimed could destabilize the country. More prosecutions could target political allies who used to be with the Khmer Rouge -- as he was himself, before defecting.