The CIA took top al-Qa'ida suspects close "to the point of death" by drowning them in baths during interrogation sessions in the years that followed the September 11 attacks, a security source has said.
The description of the torture meted out to at least two leading al-Qa'ida suspects, including the alleged 9/11 mastermind Khalid Sheikh Mohammed, far exceeds the conventional understanding of waterboarding, or "simulated drowning" so far admitted by the CIA.
"They weren't just pouring water over their heads or over a cloth," said the source, who has first-hand knowledge of the period.
"They were holding them under water until the point of death, with a doctor present to make sure they did not go too far. This was real torture," the source added.
The account of extreme CIA interrogation comes as the US Senate prepares to publish a declassified version of its so-called 'Torture Report' - a 3,600-page document based on a review of several million classified CIA documents. Publication of the report is currently being held up by a dispute over how much of the 480-page public summary should remain classified, but it is expected to be published within weeks.
A second source who is familiar with the Senate report said that it contained several unflinching accounts of some CIA interrogations which, the source predicted, would "deeply shock" the general public.
Dianne Feinstein, the Democrat chair of the Senate Intelligence Committee that wrote the report has promised that it will expose "brutality that stands in stark contrast to our values as a nation". The Senate report is understood to accuse the CIA of lying and of grossly exaggerating the usefulness of torture.
Its publication is being angrily opposed by many senior Republicans, former CIA operatives and Bush-era officials, including the former US vice-president Dick Cheney, who argue that is it poorly researched and politically motivated.
The CIA has previously admitted that it used "black sites" to subject at least three high-value al-Qa'ida detainees to "enhanced interrogation" - namely Mohammed, the alleged USS Cole bomber Abd al Rahim al Nashiri and alleged senior Bin Laden aide Abu Zubaydah. (© Daily Telegraph, London)