The 779 prisoners at the US detention facility in Guantanamo, Cuba, included around 30 people suffering from serious mental disorders, the Spanish daily El Pais and other newspapers reported Tuesday.
El Pais cited US Defence Department documents obtained by WikiLeaks.
The documents describe cases of prisoners suffering from schizophrenia, paranoia, depression, drug addiction or severe personality disorders, DPA reported.
The inmates included a 89-year-old man suffering from senile dementia who was kept at the prison camp for four months.
Another prisoner, a 40-year-old Afghan, drank shampoo, ate his own faeces and covered his naked body with excrement.
He was transferred to Afghanistan in 2002 after being kept at Guantanamo for eight months. His condition "makes it difficult or impossible to obtain information during questioning," the Defence Department concluded.
Most of the mentally ill prisoners were confined at Guantanamo for several years before being sent to other countries.
The WikiLeaks documents give the impression of extremely violent relations between inmates and their guards, El Pais observed.
The documents describe inmates as constantly attacking prison officials in different ways, ranging from throwing food or urine to trying to break a guard's arm.
Inmates were punished even for lesser "offences," such as fasting, writing on the wall, making holes in walls or underlining a library book. The documents do not reveal what the punishments consisted of.
Prisoners made dozens of suicide attempts, some of which were successful.
About 170 prisoners still remain at Guantanamo.
The US government has condemned the publication of such "sensitive information" and has said some of the information does not represent the government's "current view" of the detainees.
US President Barack Obama pledged before coming to power to close down the prison camp and transfer detainees for prosecution to the US civilian court system. However the camp remains open. More than 600 detainees have been transferred to other countries since the prison opened in 2002.
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