The US State Department's former number two said the practice of waterboarding terror suspects was torture and he hoped he would have had the courage to resign had he known the CIA was using the interrogation technique.
However, Richard Armitage, the deputy secretary of state during the Bush administration, told Al Jazeera English television he did not believe CIA officials who took part in waterboarding and other forms of harsh interrogation should be prosecuted.
The CIA has acknowledged using waterboarding which simulates drowning, on three high-level terror detainees in 2002 and 2003, with the permission of the White House and the US Justice Department.
"I hope, had I known about it at the time I was serving, I would've had the courage to resign. But I don't know. It's in hindsight now," Mr Armitage said.
Mr Armitage left the government after George Bush was re-elected in November 2004. He announced he was leaving the day after the resignation of Colin Powell, Mr Bush's Secretary of State.
Mr Armitage told Al Jazeera that no one at the State Department knew prisoners were being abused until the Abu Ghraib scandal revealed it to the world in April 2004.
Congress was at least as much to blame as Bush administration officials for prisoner abuse, he said, because politicians failed to oversee the detention, interrogation and rendition programmes, which transported prisoners to other countries where mistreatment was probable.
"They weren't doing their job," he said.
Elsewhere, US attorney general Eric Holder told a military academy audience that some people engaged in the war against terror broke the law.
Mr Holder did not specify the target of the criticism levelled in prepared remarks for a conference at the US Military Academy at West Point, New York, but praised military lawyers in the Judge Advocate General Corps for their work representing terror detainees.
"In our current struggle against international terrorism, when others surrendered faithful obedience to the law to the circumstances of the time, it was the brave men and women in the JAG corps who stood up against the tides, many times risking their careers to do so," Mr Holder said.
The speech came a day before a court deadline for the Obama administration to release all or parts of key Bush administration memos detailing which tough interrogation techniques were acceptable against terror suspects.
Mr Holder insisted that even when the government must act in secrecy for national security reasons, "we must be most vigilant in relying on the rule of law to govern our conduct".