CIA interrogators used the controverisal waterboarding technique 183 times on Khalid Sheikh Mohammed, the mastermind behind the September 11, 2001, attacks and 83 times on another al-Qaeda suspect, according to The New York Times.
A 2005 Justice Department memorandum revealed that the simulated drowning technique was used on Mohammed 183 times in March 2003.
Abu Zubaydah, the first prisoner questioned in the CIA’s overseas detention programme in August 2002, was waterboarded 83 times, although a former CIA officer had told news organisations that he had been subjected to only 35 seconds under water before agreeing to tell everything he knew.
President Barack Obama has banned the use of waterboarding, overturning a Bush Administration policy that it did not constitute torture.
The memo is one of four authorising “harsh interrogation” that were declassified by the Obama Administration last week. They show that the CIA based more than 3,000 intelligence reports on the questioning of “high-value” terror suspects from September 11, 2001, to April 2003.
According to The New York Times, some copies of the memo on Mohammed appeared to have the number of waterboardings used on him redacted while others did not.
A footnote to another 2005 Justice Department memo said that waterboarding was used both more frequently and with a greater volume of water than the CIA rules permitted, the newspaper claimed, while a separate footnote said that the use of the harshest techniques appeared to have been “unnecessary” in Abu Zubaydah’s case.
On Saturday, The New York Times claimed that Abu Zubaydah had already given all the information he knew before he was subjected to waterboarding.
Officials in the Bush Administration had claimed that harsh interrogation techniques were necessary to get information but the number of times Mohammed was subjected to waterboarding will raise questions about its efficacy and about assertions from officials that the methods were used under strict guidelines.
Mr Obama, who will make his first visit to the CIA headquarters today, does not intend to prosecute Bush Administration officials who devised the policies that led to the harsh interrogation techniques, the White House Chief of Staff, Rahm Emanuel, said on Sunday.
Mr Obama has already made clear that he did not believe that those who carried out the interrogations should be prosecuted. Announcing the release of the documents last week, he said: "It is our intention to assure those who carried out their duties relying in good faith upon legal advice from the Department of Justice that they will not be subject to prosecution."
He did not mention the officials but Mr Emanuel told ABC television that the President did not want them prosecuted. Mr Obama believed that they "should not be prosecuted either and that’s not the place that we go".