Mr Obama has banned the use of controversial interrogation techniques
US President Barack Obama's decision not to prosecute CIA agents who used torture tactics is a violation of international law, a UN expert says.
The UN special rapporteur on torture, Manfred Nowak, says the US is bound under the UN Convention against Torture to prosecute those who engage in it.
Mr Obama released four "torture memos" outlining harsh interrogation methods sanctioned by the Bush administration.
Mr Nowak has called for an independent review and compensation for victims.
"The United States, like all other states that are part of the UN convention against torture, is committed to conducting criminal investigations of torture and to bringing all persons against whom there is sound evidence to court," Mr Nowak told the Austrian daily Der Standard.
The memos approved techniques including simulated drowning, week-long sleep deprivation, forced nudity, and the use of painful positions.
Mr Obama on Thursday said he would not prosecute under anti-torture laws CIA personnel who relied in good faith on Bush administration legal opinions issued after the 11 September attacks.
Aimed at simulating sensation of drowning. Used on alleged 9/11 planner Khalid Sheikh Mohammed
Harmless insect to be placed with suspect in 'confinement box', suspect to be told the insect would sting. Approved for Abu Zubaydah, but not used
Detainee slammed repeatedly into false wall to create sound and shock
Detainee shackled stading up. Used often, once for 180 hours
Mr Nowak - who is due to travel to Washington to meet with officials - said that could be a mitigating factor, but does not absolve those involved.
"The fact that you carried out an order doesn't relieve you of your responsibility," he was quoted as saying by AP news agency.
Mr Nowak, an Austrian law professor, said US courts could still try those suspected of carrying out torture, as Mr Obama has not sought an amnesty law for affected CIA personnel.
He called for an investigation by an independent commission before suspects were tried and said it was important that all victims receive compensation.
Human rights groups have criticised President Obama's decision to protect CIA interrogators, saying charges were necessary to prevent future abuses and hold people accountable.
President Obama banned the use of the controversial interrogation techniques in his first week in office.