The Obama administration in the USA has published secret memos detailing the legal justification for the CIA interrogation programme in the Bush era, which critics say amounted to making torture legitimate.
The development is seen as a victory for human rights campaigners.
The new president has said that the techniques will not be used again and that "the USA rejects the use of torture".
But he has also guaranteed that no CIA employees will be prosecuted for their role in Bush-era interrogations, because they were acting "under orders" and "in good faith".
Anti-torture campaigners say that this sets a dangerous precedent and does not go far enough, though they welcomed the release of the four secret documents and the government's commitment to opposing torture.
Amnesty International said the Department of Justice appeared to be offering a "get-out-of-jail-free card" to individuals who were involved in acts of torture.
"The Bottom line here is you've had crimes committed," Amnesty International analyst Tom Parker told the BBC.
"These are criminal acts. Torture is illegal under American law, it's illegal under international law. America has an international obligation to prosecute the individuals who carry out these kind of acts."
The International Bar Association (IBA) also says that President Obama appears to have received "wrong legal advice" on prosecutions.
Allies of the Bush administration are furious about the move, claiming it undermines the fight against terror. Obama's supporters say the opposite - that only the USA's own moral legitimacy can strengthen the case against terror tactics by others.
News agencies report that some in the CIA wanted parts of the secret memos to be blacked out, fearing that full disclosure will trigger private lawsuits against agents.
The release of the memos stems from a persistent campaign by the American Civil Liberties Union (ACLU) and other human rights groups, nationally and world-wide.
Three of the newly released documents were written in May 2005 by the then acting head of the Justice Department's Office of Legal Counsel (OLC), Stephen Bradbury.
The BBC says they gave legal support for the combined use of various coercive techniques, and concluded that the CIA's methods were not "cruel, inhuman or degrading" under international law.
The fourth document, dating from 1 August 2002, was written by OLC lawyer John Yoo and signed by his colleague Jay Bybee.
This document contained legal authorisation for a list of specific harsh interrogation techniques, including pushing detainees against a wall, facial slaps, cramped confinement, stress positions and sleep deprivation.
The memo also authorised the use of "waterboarding", or simulated drowning, and the placing of a detainee into a confined space with an insect.
President Obama declared: "I believe that exceptional circumstances surround these memos and require their release. Withholding these memos would only serve to deny facts that have been in the public domain for some time."