CIA director Michael Hayden for the first time admitted publicly Tuesday that the agency had used “waterboarding,” or simulated drowning, in interrogations of three top Al-Qaeda detainees nearly five years ago.

The technique, which critics say is tantamount to torture, was used on Khalid Sheikh Mohammed, Abu Zubaydah and Abd Al-Rahim al-Nashiri at a time when further catastrophic attacks on the United States were believed to be imminent, Hayden said.

“Let me make it very clear and to state so officially in front of this committee that waterboarding has been used on only three detainees,” he told members of the Senate Intelligence Committee.

“It was used on Khalid Sheikh Mohammed. It was used on Abu Zubaydah. And it was used on Nashiri.”

Mohammed has claimed to be the operational mastermind of the September 11, 2001 attacks. Abu Zubaydah is alleged to have been an aide to Al-Qaeda leader Osama bin Laden. And al-Nashiri is alleged to have been the operational commander of the suicide attack on the USS Cole in Yemen in 2000.

All three were initially held and interrogated at secret CIA-run detention centers overseas before being transferred in 2006 to a military-run facility at Guantanamo Bay, Cuba.

Hayden’s remarks were the first direct official admission that agency interrogators had used “waterboarding” in questioning “war on terror” detainees.

The admission came amid a long-running battle between the administration and members of Congress over so-called “enhanced” or coercive interrogation techniques used by the CIA.

Senator Dick Durbin, a Democrat from Illinois, sent a letter to Attorney General Michael Mukasey Tuesday, demanding a Justice Department investigation into whether the use of waterboarding violated the law.

Human Rights Watch said Hayden’s remarks were “an explicit admission of criminal activity.”

“General Hayden’s testimony gives the lie to all of the administration’s past protestions that the CIA has not employed torture,” said Joanne Mariner, a spokeswoman for the New York-based rights monitor.

“Waterboarding is torture, and torture is a crime.”

Mukasey told Congress last week that the CIA no longer uses “waterboarding” and that it was not “currently” an authorized interrogation technique.

But he refused to say whether waterboarding is torture.

“There are some circumstances where current law would appear clearly to prohibit waterboarding’s use. Other circumstances would present a far closer question.”

The New York Times disclosed in December that videotapes of interrogations of Abu Zubaydah and Al-Nashiri were destroyed in 2005 on orders of a senior agency official.

In his testimony, Hayden suggested that the CIA no longer needed to use “waterboarding” in interrogations because circumstances had changed since the period following the September 11, 2001 attacks on the United States.

“We used it against these three high-value detainees because of the circumstances of the time. Very critical to those circumstances was the belief that additional catastrophic attacks against the homeland were imminent.

“In addition to that, my agency and our community writ large had limited knowledge about Al-Qaeda and its workings. Those two realities have changed,” he said.

He said the technique had not been used in almost five years.

But Hayden defended the CIA’s use of coercive interrogation techniques as lawful and opposed moves by Congress to make the agency follow rules of interrogation set forth in the Army Field Manual.

He said “it would make no more sense to apply the Army Field Manual to CIA — the Army Field Manual on interrogations — than it would be to take the Army Field Manual on grooming and apply it to my agency, or the Army Field Manual on recruiting and apply it to my agency, or, for that matter, take the Army Field Manual on sexual orientation and apply it to my agency.”

Retired Admiral Mike McConnell, the director of national intelligence, likewise suggested that the circumstances determine whether waterboarding is lawful.

“If there was a reason to use such a technique, you would have to make a judgment on the circumstances and the situation regarding the specifics of the event,” he said.