WASHINGTON: US President Barack Obama has assured CIA agents involved in tough terror interrogations they will not be prosecuted as he released graphic memos detailing methods approved by the Bush White House.

In documents published on Thursday, George W. Bush-era legal officials argued that the tactics such as simulated drowning, face slapping and sleep deprivation did not amount to torture.

"This is a time for reflection, not retribution," Obama said. "We have been through a dark and painful chapter in our history. But at a time of great challenges and disturbing disunity, nothing will be gained by spending our time and energy laying blame for the past."