Former Khmer Rouge head of state Khieu Samphan went before Cambodia's genocide tribunal for a pre-trial hearing Wednesday, where famed French lawyer Jacques Verges branded his detention "illegal."

The controversial Verges, who has defended some of the world's most infamous figures, said he was "indignant" to discover the 16,000 pages of court documents had not been translated into French, one of the court's three official languages.

"The defence is not possible," Verges, whose clients have included Nazi war criminal Klaus Barbie and Venezuelan terrorist "Carlos the Jackal," told reporters after Khieu Samphan appeared before the UN-backed tribunal to appeal against his detention without bail.

"I am unable to know what my client is charged with," the flamboyant lawyer shouted in French to reporters outside the court, adding: "This is unheard of, except in dictatorships."

"His detention is illegal because it has been ordered from a file to which his lawyers did not have access," said the lawyer nicknamed "The Devil's Advocate" for representing infamous defendants.

Khieu Samphan, who was detained by the court in November on charges of war crimes and crimes against humanity, earlier listened stony-faced as head judge Prak Kimsan read out the background of the case against him.

Khieu Samphan then told the court, which was set up to try former Khmer Rouge leaders for genocide and crimes against humanity during their brutal 1975-1979 rule, he had lived in poverty for the last 10 years.

"I have had no job since leaving the jungle. (I have) only my wife, who struggles to feed me, and my family," Khieu Samphan said in Khmer, referring to his 1998 defection from the then-dying Khmer Rouge guerrilla movement based in the remote northwest.

Khieu Samphan, who court documents say is 76, was dressed in a light-grey shirt and trousers and spoke in a quiet, hoarse voice as he addressed the three Cambodian and two foreign judges, an AFP reporter at the court said.

The court later went into a closed-door session which was later postponed. The judges were to make a statement later.

Prosecutor Chea Leang said the postponement was "regrettable".

"Everyone has been waiting for justice for so long, and the victims want the hearing to take place soon," she said.

"The translation will prolong the proceeding of the hearing," she added.

A fierce anti-colonialist, Verges, 83, who was born in Thailand, reportedly befriended Khieu Samphan and other future Khmer Rouge leaders while at university in Paris in the 1950s.

In documents submitted to the court at the time of Khieu Samphan's detention, the prosecution said releasing him on bail could provoke public anger, possibly putting the elderly defendant at risk of revenge attacks.

"If he remains at liberty, this could provoke the anger of victims and the public."

Defence lawyers argue that Khieu Samphan had no real power under the regime and in appeal documents lodged in December they petitioned for a dismissal of the detention order "because Mr Khieu Samphan is not guilty."

"He was simply a head of state in name only," they said in the documents.

Khieu Samphan has never denied the bloodletting under the Khmer Rouge but the former head of state of Cambodia's radical communist government has never admitted to a role in the regime's excesses.

Up to two million people are believed to have been executed or died of starvation and overwork as the communist regime emptied Cambodia's cities, exiling millions to vast collective farms in a bid to forge an agrarian utopia.

Khieu Samphan, the last of five top regime leaders to be arrested and detained by the tribunal, has repeatedly denied his involvement in the atrocities.

Cambodia's genocide tribunal convened in 2006 after nearly a decade of haggling between the government and the United Nations.