The No. 2 leader of Cambodia's brutal Khmer Rouge regime told a court he and his comrades were not "bad people," denying responsibility Monday for the deaths of an estimated 1.7 million Cambodians during their 1970s rule.

Nuon Chea's defiant statements came as the UN-backed tribunal began questioning him for the first time since the long-awaited trial of three top regime leaders began late last month. Nuon Chea and two other Khmer Rouge leaders are accused of crimes against humanity, genocide, religious persecution, homicide and torture stemming from the group's 1975-79 reign of terror. All have denied wrongdoing.

The trusted deputy of the late Pol Pot, Nuon Chea blamed neighbouring Vietnam for the atrocities that occurred, reiterating long-standing Khmer Rouge's claims that the mass graves discovered subsequently were of people killed by Vietnamese armed forces.

This week the court is expected to focus on charges involving the forced movement of people and crimes against humanity. After the Khmer Rouge captured Phnom Penh on April 17, 1975, they began moving an estimated 1 million people -- even hospital patients -- from the capital into the countryside in an effort to create a communist agrarian utopia.

After a court clerk read a background of the Khmer Rouge and the three defendants, Nuon Chea defended the notoriously brutal movement.

"I don't want the next generation to misunderstand history. I don't want them to believe the Khmer Rouge are bad people, are criminals," Nuon Chea said. "Nothing is true about that."

The 85-year-old one-time chief ideologist for the communist movement insisted that no Cambodian was responsible for atrocities during the Khmer Rouge's reign.

"These war crimes and crimes against humanity were not committed by the Cambodian people," Nuon Chea said. "It was the Vietnamese who killed Cambodians."

Former Khmer Rouge leader Nuon Chea, centre, sits in the court room at the Extraordinary Chambers in the Courts of Cambodia on the outskirts of Phnom Penh on Monday. (Nhet Sokheng/ECCC/Reuters)

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

When a judge asked about the background of Khmer Rouge party, Nuon Chea said it had been set up to liberate the country from the rich and powerful.

Sought adjournments

Later, Nuon Chea twice asked the court to adjourn early, complaining of heart problems and breathlessness. Judge Nil Nonn then adjourned proceedings until Tuesday.

The other defendants are Khieu Samphan, an 80-year-old former head of state who also told the court in November he bore no responsibility for atrocities, and 86-year-old Ieng Sary, who has said he will not participate in the trial until a ruling is issued on a pardon he received in 1996. The tribunal previously ruled the pardon does not cover its indictment against him.

There is concern that the accused could pass away before justice is achieved.

Pol Pot died in 1998 in Cambodia's jungles, and a fourth defendant, 79-year-old Ieng Thirith, was ruled unfit to stand trial because she has Alzheimer's disease. She is Ieng Sary's wife and was the regime's minister for social affairs.

The tribunal is seeking justice on behalf of the estimated quarter of Cambodia's population who died from executions, starvation, disease and overwork under the Khmer Rouge.

"This is the first time the accused persons will be asked questions in a public hearing about their role in the events that led to the takeover of Phnom Penh on 17 April 1975 and about the policies of the Khmer Rouge," tribunal spokesman Lars Olsen told The Associated Press.

Olsen said the initial testimony will take several days. After the accused have been questioned, witnesses and civil parties will be also called to testify, he said.

Only one conviction

So far the UN-backed tribunal, established in 2006, has tried just one case, convicting Kaing Guek Eav, the former head of the Khmer Rouge's notorious S-21 prison, last year and sentencing him to 35 years in prison for war crimes, crimes against humanity and other offences. His sentence was reduced to 19 years due to time served and other technicalities.

That case was seen as much simpler than those currently before the court, in part because Kaing Guek Eav confessed to his crimes.

Chum Mey, 80, one of only two survivors of the S-21 prison, said he doesn't believe the three defendants will tell the truth about what happened in the 1970s.

"During last month's sessions we heard them say only that their regime was good and worked for the entire people," Chum Mey said.