WASHINGTON - THE United States tortured an alleged plotter of the September 11, 2001 terror plot held at the Guantanamo detention center, the Washington Post reported on Wednesday, citing a Pentagon official.

Ms Susan Crawford, 61, who is the official charged making a decision about whether to bring Guantanamo detainees to trial, told The Post that US interrogators had tortured Saudi terror suspect Mohammed al-Qahtani.

'We tortured Qahtani,' the daily wrote quoting Ms Crawford, who is the first senior Bush administration official to publicly state that a detainee was tortured.

'His treatment met the legal definition of torture. And that's why I did not refer the case' for prosecution, she said.

Ms Crawford said US military interrogators repeatedly subjected Qahtani, 30, to sustained isolation, sleep deprivation, nudity and prolonged exposure to cold, leaving him in a 'life-threatening condition'.

A Pentagon spokesman said the interrogation techniques used on Qahtani were authorised by Defence Secretary Donald Rumsfeld and subsequent reviews found them to be lawful.

'However, the department did adopt a new and more restrictive policy as well as improved oversight procedures for interrogations and detention operations,' said Mr Bryan Whitman.

'While some of the aggressive questioning techniques used on Qahtani were permissible at the time, they are no longer allowed in accordance with the updated army field manual,' he said.

Meanwhile, the White House reiterated its position that it has not tortured detainees, and said the case in question was a Pentagon matter.

'It has never been the policy of this president or this administration to torture,' said White House spokesman Dana Perino, noting that the Department of Defence had already issued a statement about the article.

'As I understand it, the commander-in-chief should not be commenting on cases where the government is bringing a case against a detainee,' she said.

'It would be inappropriate to do so from the White House.'

Qahtani, alleged to be the 20th hijacker in the September 11 attacks, was denied entry to the United States one month before the attacks but was captured in Afghanistan and flown to Guantanamo in January 2002.

He was interrogated over 50 days from November 2002 to January 2003, though he was held in isolation until April 2003, according to the Post.

'The techniques they used were all authorised, but the manner in which they applied them was overly aggressive and too persistent,' Ms Crawford told the newspaper.

'You think of torture, you think of some horrendous physical act done to an individual. This was not any one particular act; this was just a combination of things that had a medical impact on him, that hurt his health,' she said.

'It was abusive and uncalled for. And coercive. Clearly coercive. It was that medical impact that pushed me over the edge' to call it torture, the ex-judge said Ms Crawford dismissed war crimes charges against him in May 2008.

Ms Crawford, 61, is a retired judge who previously worked for the Pentagon.

Defence Secretary Robert Gates named her the top authority on whether to try Guantanamo detainees in February 2007. -- AFP