Now aged 82 and in failing health following an earlier stroke, officials say Nuon Chea will receive regular visits from doctors, as well as access to cable television while in detention.
He is being held in the same block and the same conditions as Kaing Guek Eav, also known as Duch, who headed the Khmer Rouge S-21 torture and interrogation centre, based in the former Tuol Sleng high school.
"We have been informed by medical doctors and detention guards that he is in good spirits," tribunal spokesman Reach Sambath told reporters.
Asked about the conditions the two men were being held under, he said: "We provide him with the best services we can.''
"Even Cambodian people in general do not get the kind of services they are getting… But we want them to live as long as possible so that they can defend themselves and confront with the law."
Nuon Chea, who became the so-called Brother Number Two of the Khmer Rouge, is the most senior surviving member of the former regime.
Pol Pot, the group's leader, died in his jungle hideout in 1998.
His military commander, Ta Mok, nicknamed "the Butcher", died in government custody in 2006.
Two other senior Khmer Rouge leaders - Ieng Sary, the former foreign minister, and Khieu Samphan, the former head of state - currently live freely but are also widely believed to be on the prosecutors' list.
|The Khmer Rouge are blamed for the death of |
up to a fifth of Cambodia's population [Reuters]
Up to 2 million people, or about a fifth of Cambodia's then population, died during the Khmer Rouge's rule over Cambodia between 1975 and 1979.
Most died of starvation, overwork, torture or were executed as perceived enemies of the state.
Nuon Chea has consistently denied any responsibility for the killings, although he has said he is ready to face the tribunal
"My father is happy to shed light on the Khmer Rouge regime for the world and people to understand," his son, Nuon Say, told reporters following Wednesday's arrest.
Duch however is on record as having told Cambodian government investigators that Nuon Chea had "direct command" over S-21 where an estimated 14,000 people were tortured and executed.
Trials in the UN-backed tribunal are expected to begin in early 2008.