A Saudi Arabian national held at the US prison facility in Guantanamo Bay was tortured by US military personnel over his alleged involvement in the September 11, 2001 attacks, a senior US official has said.
Mohammed al-Qahtani suffered techniques including sustained isolation, sleep deprivation, nudity and prolonged exposure to cold, Susan Crawford, told the Washington Post newspaper on Wednesday.
Crawford, the Bush administration official in charge of deciding whether to bring detainees to trial, said the torture left al-Qahtani in a "life-threatening condition".
"This was not any one particular act; this was just a combination of things that had a medical impact on him," she said.
"It was abusive and uncalled for. And coercive."
She said she could not recommend he face prosecution as he had been subjected to torture.
Crawford said a decision on what to do with al-Qahtani was yet to be made as he was still considered "a very dangerous man".
"What do you do with him now if you don't charge him and try him? I would be hesitant to say, 'Let him go'," she told the paper.
Both George Bush, the US president, and Dick Cheney, the US vice-president, have rejected allegations that the US tortured suspects being held at the US facility in Guantanamo, Cuba.
There has been widespread controversy over the use of the interrogation technique of "waterboarding", which simulates drowning, and which the US Central Intelligence Agency (CIA) admitted in February last year had been used on three detainees at Guantanamo.
A confession made by Khalid Sheikh Mohammed, the alleged mastermind of the September 11 attacks, was reportedly obtained using the method.
Geoff Morrell, a spokesman for the Pentagon, told the Post that it took any allegations of abuse "seriously" but that investigations into their detention operations on detainees, including al-Qahtani, found that the "special" techniques used on him "were lawful".
Morell said that the Pentagon had adopted "new and more restrictive" policies for interrogation following the reviews.
"Some of the aggressive questioning techniques used on al-Qahtani, although permissible at the time, are no longer allowed in the updated army field manual," he told the paper.
Qahtani, sometimes alleged to be the so-called "20th hijacker" of the September 11 attacks, was denied entry into the US in August 2001 and captured in Afghanistan in January 2002 before being transported to Guantanamo Bay, the paper said.
War crimes charges against him were dismissed in May last year by Crawford, but military prosecutors said in November that they would seek to refile charges based on subsequent interrogations that did not employ the harsher techniques, the paper said.
About 255 men are still being held in Guantanamo Bay, mostly al-Qaeda and Taliban suspects captured during the US-led invasion of Afghanistan.
Barack Obama, the US president-elect, is expected to issue an executive order to close the facility.
The fate of the detainees remains uncertain until US officials resolve legal and logistical problems, including where those not set for trial could be sent.