Tough interrogation spread outwards from Guantanamo, the report said
US government backing for the CIA's harsh interrogation methods set the tone for abuses by US troops towards detainees in Iraq, a US report says.
It was not appropriate simply to blame low-ranking officers for what occurred at Abu Ghraib prison, the report by the Senate Armed Services Committee said.
Top officials had sent the message that such acts were appropriate, it stated.
The report follows the release of Bush-era memos that justify the use of what some critics say amounts to torture.
The memos detail a range of methods the CIA could use on terrorism suspects under the previous government.
These included week-long sleep deprivation, forced nudity and the use of painful positions, as well as water-boarding - a technique which simulates drowning.
'Erosion in standards'
The Senate committee's 263-page report was entitled: "Inquiry into the treatment of detainees in US custody".
It examined how the use of harsh interrogation tactics by the CIA at the Guantanamo Bay detention centre came to be approved and the effect this had on policy towards detainees elsewhere.
The report sets out how, shortly after the 11 September 2001 attacks, Pentagon officials sought information on harsh interrogation methods from specialist military trainers.
Despite warnings from military personnel that the use of these on Guantanamo detainees could backfire, 15 specific techniques were sanctioned by then Secretary of Defense Donald Rumsfeld on 2 December 2002, the report said.
What followed was "an erosion in standards dictating that detainees be treated humanely", it said.
That these techniques had been endorsed became known by US troops in Afghanistan and Iraq, setting the stage for the abuses that took place at Abu Ghraib and elsewhere, it said.
"In my judgment, the report represents a condemnation of both the Bush administration's interrogation policies and of senior administration officials who attempted to shift the blame for abuse - such as that seen at Abu Ghraib, Guantanamo Bay and Afghanistan - to low-ranking soldiers," said Senator Carl Levin, the committee chairman.
Claims that detainee abuses could be chalked up to the unauthorised acts of a "few bad apples", were simply false, he said.
"Authorisations of aggressive interrogation techniques by senior officials resulted in abuse and conveyed the message that physical pressures and degradation were appropriate treatment for detainees in US military custody," he said.
Mr Obama is under growing pressure from his own party and rights organisations not to rule out the prosecution of officials who authorised the techniques.
National Intelligence Director Dennis Blair, one of Mr Obama's top aides on national security, told staff in a letter last week that the interrogations had resulted in "high-value information".
But in a statement on Tuesday, Mr Blair said that he had strongly supported the president's declaration that harsh interrogation techniques would no longer be used, and that such methods were not needed to keep the nation safe.
"The information gained from these techniques was valuable in some instances, but there is no way of knowing whether the same information could have been obtained through other means," Mr Blair said.
"The bottom line is these techniques have hurt our image around the world, the damage they have done to our interests far outweighed whatever benefit they gave us, and they are not essential to our national security."
But some Bush administration officials have defended the policy. On Monday, former Vice-President Dick Cheney said that the techniques produced results.
He called for the release of documents demonstrating that important intelligence had been obtained through harsh interrogation.