Phnom Penh - The former "first lady" of Cambodia's genocidal Khmer Rouge regime told the UN-backed war crimes tribunal on Tuesday her accusers would be "cursed to the seventh level of hell" for implicating her in the deaths of up to 2 million people three decades ago.

Ieng Thirith, 76, faces charges of crimes against humanity allegedly committed while she was minister for social affairs during the ultra-Maoist Khmer Rouge's 1975-79 reign.

"I am not a murderer, so don't accuse me of murder otherwise you will be cursed to the seventh level of hell," she shouted in an incensed closing statement to the court.

"I am here to speak the truth and tell you I have done nothing wrong."

The former English literature professor was in the Phnom Penh court to appeal an extension of her pre-trial detention, but originally ordered her lawyers to speak on her behalf because she was "too weak" to deliver her plea.

Cambodian co-defence lawyer Phat Pouv Seng said the investigating judges had insufficient evidence to warrant Ieng Thirith's detention.

"No additional evidence linking Ieng Thirith to crimes committed during the period has been added to the case file since she was placed in pre-trial detention in November 2007," he said.

But prosecutors argued that three years of pre-trial detention was permissible according to international standards and said a suspension could lead to civil unrest and put Ieng Thirith's safety at risk.

Judges are expected to announce a ruling on the appeal later this week.

Five former Khmer Rouge leaders, including Ieng Thirith's husband and former foreign minister Ieng Sary, are currently facing trial for their roles in deaths of up to 2 million people through execution, starvation and overwork.

The group sought to transform Cambodian society into an agrarian-socialist utopia, erase history and start at "year zero."

The first stage of the trial of former Tuol Sleng torture facility chairman Kaing Guek Eav, known by his revolutionary name Duch, was held last week.

The Khmer Rouge tribunal announced on Monday that Duch's trial would resume on March 31.

He is the first detainee to be indicted for crimes against humanity.

Ieng Thirith, who is the sister-in-law of deceased Khmer Rouge leader Pol Pot, said she had no involvement with Duch and blamed fellow detainee and former head of state Nuon Chea for the deaths of millions of Cambodians.

"Everything was done by Nuon Chea," she said. "I've done the best for my nation, for the motherland."

Defence lawyers have previously sought to have Ieng Thirith released because of her apparently poor physical and mental health.

"Before the hearing today she whispered in my ear that she had not slept well for the last 10 days, so this hearing could jeopardize her health even more," Phat Pouv Seng said at a press conference after the hearing.

The Khmer Rouge tribunal was established in 2006 after a decade of negotiations between the UN and the Cambodian Government and consists of international and domestic judges, prosecutors and defence lawyers. (dpa)