The CIA waterboarded two al-Qaida terror suspects a total of 266 times, according to a report that suggests the use of the torture technique was much more extensive than previously thought.

    The documents showed waterboarding was used 183 times on Khalid Sheikh Mohammed, who admitted planning the 9/11 attacks, the New York Times reported today.

    The US Justice Department memos released last Thursday showed that waterboarding, which the US now admits is torture, was used 83 times on the alleged al-Qaida senior commander Abu Zubaydah, the paper said. A former CIA officer claimed in 2007 that Zubaydah was subjected to the simulated drowning technique for only 35 seconds.

    The numbers were removed from most of the memos over the weekend. But bloggers, including Marcy Wheeler from empytwheel, discovered that the figure had not been blanked out from one of the memos.

    Barack Obama has banned waterboarding and overturned a Bush administration policy that it did not amount to torture.

    The president did not intend to prosecute Bush administration officials who devised the policies that led to such interrogations, his chief of staff, Rahm Emanuel, said yesterday.

    Asked on Sunday about the fate of those officials, Emanuel told ABC's This Week programme that Obama believed they "should not be prosecuted either and that's not the place that we go".

    Michael Hayden, who led the CIA under Bush, said the public release of the memos would make it harder to get useful information from suspected terrorists being detained by the US.

    "I think that teaching our enemies our outer limits, by taking techniques off the table, we have made it more difficult in a whole host of circumstances I can imagine, more difficult for CIA officers to defend the nation," Hayden said on Fox News Sunday.

    He disputed an article in the New York Times on Saturday that said Zubaydah had revealed nothing new after being waterboarded, saying that he believed that after unspecified "techniques" were used Zubaydah revealed information that led to the capture of another terrorist suspect, Ramzi Binalshibh.

    One of the released memos was a 2002 justice department briefing memo written by assistant attorney general Jay Bybee and sent to John Rizzo, the acting general counsel for the CIA, spelling out in detail how waterboarding should be practised. It specifically refers to the interrogation of Zubaydah using the water technique.

    "In this procedure," Bybee said, "the individual is bound securely to an inclined bench, which is approximately four feet by seven feet. The individual's feet are generally elevated. A cloth is placed over the forehead and eyes. Water is then applied to the cloth in a controlled manner. As this is done the cloth is lowered until it covers both the nose and the mouth. Once the cloth is saturated and completely covers the mouth and nose, air flow is slightly restricted for 20 to 40 seconds ... this causes an increase in carbon dioxide level in the individual's blood.

    "This increase in the carbon dioxide level stimulates increased efforts to breath. This effect plus the cloth produces the perception of 'suffocation and incipient panic', ie the perception of drowning. The individual does not breathe any water into his lungs."

    After the 20 to 40 seconds, the cloth is lifted and the individual is allowed three or four full breaths before the procedure is repeated.

    The memo went on to say that "we also understand that a medical expert will be present throughout this phase and the procedure will be stopped if deemed medically necessary to prevent severe mental or physical harm to Zubaydah".

    A footnote to another 2005 justice department memo released last week said waterboarding was used both more frequently and with a greater volume of water than the CIA rules permitted.