George Bush defended waterboarding as an interrogation technique that helped "save lives" in the US.
The new United Nations expert on torture has urged the United States to conduct a full investigation into torture allegations of detainees under the former administration of George Bush, the then US president.
Juan Ernesto Mendez told the Reuters news agency that the US should prosecute offenders and senior officials who ordered the abuse in Iraq, Afghanistan and the Guantanamo Bay detention centre in Cuba.
"The United States has a duty to investigate every act of torture. Unfortunately, we haven't seen much in the way of accountability," Mendez said in his first interview with an international media organisation since taking up the post two weeks ago.
"There has to be a more serious inquiry into what happened and by whose orders. It doesn't need to be seen to be partisan or vindictive, just an obligation to follow where the evidence leads," he added.
Mendez, who was himself a victim of prison torture during Argentina's dictatorship in the 1970s, also said he will visit Iraq and the Guantanamo prison to conduct his own probe of the "very widespread practice of torture".
Mendez dismissed as "very disingenuous" comments by Bush, who in his recently published memoir "Decision Points" strongly defends the use of waterboarding as crucial to his efforts to prevent a repeat of the September 11, 2001 attacks.
Bush's approval of the simulated drowning technique used by CIA personnel to wrench information from Al-Qaeda suspects is one of his most controversial decisions during his eight years in office.
Human rights violations
Amnesty International said last week that the United States must prosecute Bush for torture if his admission to authorising waterboarding, which Obama outlawed shortly after taking office in 2008, holds true.
Mendez's call for US accountability comes less than two weeks after the US faced the United Nations Human Rights Council over accusations of human rights violations for the first time.
Council members in Geneva, Switzerland, levelled a barrage of criticisms at the US on November 5, calling for the closure of the Guantanamo Bay prison and for investigations into alleged torture by US troops abroad.
The US vigorously defended its human rights record, with Harold Koh, a US state department legal adviser, telling a UN council: "Let there be no doubt, the United States does not torture and it will not torture."
He said: "Between Iraq, Afghanistan and Guantanamo we have conducted hundreds of investigations regarding detainee abuse allegations and those have led to hundreds of disciplinary actions."
But Mendez criticised previous investigations into torture allegations, saying they were limited in scope. He said congressional inquiries focused on the Pentagon rather than the CIA.
CIA tapes destroyed
Last week, the US Justice Department announced that no CIA personnel will face criminal charges for destroying videotapes of harsh interrogations of 'terrorism' suspects.
The probe was launched in January 2008 by Michael Mukasey, the US Attorney General, after revelations that the CIA in 2005 had destroyed hundreds of hours of videotapes of the interrogations of Abu Zubaydah and Abd al-Rahim al-Nashiri, two alleged Al-Qaeda suspects held in Guantanamo Bay.
Zubaydah was one of three suspects who was subjected to waterboarding. It was believed that the tapes included footage of the waterboarding.
The interrogations took place in 2002 and the CIA said that it acted lawfully in destroying the tapes because it needed to guard against leaks that could endanger interrogators. Critics accused the agency of covering up illegal acts.
"There is a lot more to the story than has been revealed. It is important to get to the bottom of what happened and under whose orders, and if necessary to bring charges," he added.
Meanwhile, the British government is to compensate former detainees in the Guantanamo Bay detention facility who accused UK security forces of being complicit in their torture overseas.
Ken Clarke, the British justice minister, said on Tuesday that the government had "agreed a mediated settlement of the civil damages claims" but that the details would remain confidential.