A former US official has accused the administration of George Bush, the former president, of authorizing "unprecedented" acts of abuse during the interrogation of detainees.
Phillip Zelikow told a US senate hearing on torture practices that the Bush administration was guilty of a "collective failure" over the interrogation of "war on terror" detainees.
"The US government over the past seven years adopted an unprecedented program in American history of cruelly calculated dehumanizing abuse and physical torment to extract information," Zelikow said on Wednesday.
"This was a mistake, perhaps disastrous one. It was a collective failure in which a number of officials and members of congress and staffers of both parties played a part, endorsing a CIA program of physical coercion."
The Bush administration has been widely criticized for allowing the use of "waterboarding", which simulates the sensation of drowning, sleep deprivation and other interrogation methods, all practices heavily criticized by human rights groups.
Zelikow, who served as an aide to Condoleezza Rice, the former US secretary of state, also testified that in 2006, former administration officials sought to collect and destroy copies of a memo he wrote opposing those methods.
"I heard the memo was not considered appropriate for further discussion and that copies of my memo should be collected and destroyed."
The hearings come as Barack Obama, the US president, challenged the Pentagon's planned release of photos depicting abuse of detainees in Afghanistan or Iraq.
The White House said he was acting on advice from military commanders that publishing the photos could endanger US troops.
Nancy Pelosi, the speaker of the US House of Representatives, has also come under recent fire over whether she knew about torture practices carried out under the Bush administration.
Recent reports allege that CIA officials had briefed an aide to Pelosi about interrogation techniques, including waterboarding, which was used hundreds of time on suspects.
Memo written by Bush-era legal officials released last month argued that tactics that also included face slapping and using insects to scare prisoners were not torture.
A Senate Intelligence Committee also released last month also said top Bush officials, such as Condoleezza Rice, then national security adviser, and Dick Cheney, the former vice-president, had approved the CIA's interrogation program, including waterboarding, in 2002.
Rice has denied she approved the torture of detainees.
The Obama administration has left the door open to prosecute those who authorized torture, but has said it will not charge people who carried out orders to use torture.
A U.S. flag flies above a razorwire-topped fence at the "Camp Six" detention facility at U.S. Naval Station Guantanamo Bay.