WASHINGTON (CNN) -- CIA interrogators used waterboarding at least 266 times on two top al Qaeda suspects, according to a Bush-era Justice Department memo released by the Obama administration.
Khalid Sheikh Mohammed, seen in a December sketch, was waterboarded 183 times in a month, a memo says.
The controversial technique that simulates drowning -- and which President Obama calls torture -- was used at least 83 times in August 2002 on suspected al Qaeda leader Abu Zubaydah, according to the memo.
Interrogators also waterboarded Khalid Sheikh Mohammed 183 times in March 2003. Mohammed is believed to be the mastermind behind the September 11, 2001, terrorist attacks on the United States.
Obama released the memo Thursday, saying that "exceptional circumstances surround these memos and require their release." Watch other tactics outlined in memos »
The memo, dated May 30, 2005, was from then-Deputy Assistant Attorney General Steven G. Bradbury to John Rizzo, who was acting general counsel for the CIA.
It paints a different picture from the one described by former CIA officer John Kiriakou. In a December 2007 interview with CNN, Kiriakou said Zubaydah had been waterboarded for "about 30 seconds, 35 seconds" and agreed to cooperate with interrogators the following day.
In an interview on "Fox News Sunday," Michael Hayden, who directed the CIA from 2006 to 2009, was asked about the number of times Mohammed was waterboarded.
Hayden denounced the release of the memos and did not comment on the number, saying it was his understanding that the frequency of waterboarding was among the operational details that had not been declassified. Watch one expert say tactics 'worse than Abu Ghraib' »
The 2005 memo refers to a letter that had contained the numbers as well. Part of the reference to the letter was redacted in the released memo.
Waterboarding is among the interrogation tactics that Obama has prohibited through an executive order.
The CIA also has admitted waterboarding Abd al-Rahim al-Nashiri, the first person charged in the United States for the 2000 attack on the USS Cole in Yemen that killed 17 U.S. sailors.
Obama said last week he felt comfortable releasing the classified memos because the Bush administration acknowledged using some of the practices associated with the memos, and the interrogation techniques were widely reported and have since been banned.
"Withholding these memos would only serve to deny facts that have been in the public domain for some time," Obama said in a statement. "This could contribute to an inaccurate accounting of the past, and fuel erroneous and inflammatory assumptions about actions taken by the United States."
The president applauded the work of the U.S. intelligence community and said no one who "carried out their duties relying in good faith upon legal advice from the Department of Justice" would be prosecuted.