Judges rejected the former Khmer Rouge foreign minister Ieng Sary's appeal for release from jail before his trial at Cambodia's UN-backed war crimes court, said Friday that former Khmer Rouge foreign minister must remain in jail on Friday until his trial.

The 83-year old Ieng Sary is charged with crimes against humanity and war crimes. He says life in jail at the tribunal is making him ill and asked to be released into house arrest.

"The request for release or modification of conditions of detention is rejected," said pre-trial chamber judge Prak Kimsan in a formal reading of the decision.

Detention was necessary to protect the former leader's safety, keep him from fleeing Cambodia and to preserve public order, Prak Kimsan told the court.

Ieng Sary, who has been rushed to hospital at least nine times since he was detained by the court in November 2007, shuffled in and out of the courtroom with the help of a cane.

His trial is expected to begin sometime next year.

Ieng Sary is one of five top regime cadres detained by the joint Cambodia-UN tribunal that was established in 2006, after nearly a decade of haggling over how to deliver justice for one of the 20th century's bloodiest episodes.

The court's long-awaited first trial has seen Kaing Guek Eav, better known by the alias Duch, accept responsibility for overseeing the execution of more than 15,000 people at the main Khmer Rouge prison.

Up to two million people died of starvation and overwork, or were executed, as the 1975-1979 regime emptied Cambodia's cities in its drive to create a communist utopia.

As the top Khmer Rouge diplomat, Ieng Sary was frequently the only point of contact between Cambodia's secretive communist rulers and the outside world.

He has denied any involvement in past atrocities but he was also one of the biggest public supporters of the regime's mass purges, researchers say.

Khmer Rouge leader Pol Pot died in 1998 before facing justice, and fears over the health of ageing suspects hang over the court.