CIA Director John Brennan has said unauthorized and in some cases abhorrent methods were used against terrorist suspects.
But Brennan asserted the CIA "did a lot of things right" in a time when there were "no easy answers."
Speaking on December 11 at CIA headquarters in Virginia, Brennan admitted that the actions of some officers were regrettable, and that certain interrogation practices were unauthorized.
His comments came two days after the release of a U.S. Senate report that found the CIA misled the White House and U.S. public about its harsh interrogation methods.
The report by the Senate Intelligence Committee found the CIA used more brutal techniques than it had acknowledged, sparking international outrage and calls for prosecution.
The 6,000 page report was the result of a five-year investigation by the Senate Intelligence Committee. Only an edited version of the report's 525-page executive summary was published.
It detailed the CIA's interrogation methods for suspected Al-Qaeda operatives at secret facilities in Europe and Asia in the years after the September 11, 2001 terrorist attacks against the United States.
Brennan conceded that it was "unknown and unknowable" whether the harsh interrogation methods had yielded crucial intelligence that could have been gained in any other way.
But he said there is no doubt that detainees subjected to the treatment offered "useful and valuable" information afterward.
The report said that none of the agency's "enhanced interrogations" provided crucial information.
It cited the CIA's own records, documenting in detail how waterboarding and lesser-known techniques such as "rectal feeding" were actually employed.
Brennan declined to define the techniques as torture, as President Barack Obama and the Senate intelligence committee have done.
Obama banned torture when he took office.
Brennan said the CIA was in "unchartered territory," after the September 11, 2001 terrorist attacks, with vast new powers authorized by a president bent on thwarted the next potential Al-Qaeda attack.
"We were not prepared," said Brennan, who was deputy CIA executive officer at the time. "We had little experience housing detainees, and precious few of our officers were trained interrogators."
Based on reporting by AP and Reuters