The head of the Central Intelligence Agency has acknowledged some agency interrogators used “abhorrent” unauthorised techniques in questioning terrorism suspects after the 9/11 attacks.

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CIA director John Brennan said on Thursday there was no way to determine whether the methods used produced useful intelligence, but he strongly denied the CIA misled the public.

“The agency failed to establish quickly the operational guidelines needed to govern the entire effort,” he said.

“In a limited number of cases, agency officers used interrogation techniques that had not been authorised, were abhorrent and rightly should be repudiated by all, and we fell short when it came to holding some officers accountable for their mistakes,” he said.

However, Mr Brennan also defended the agency, saying the torture techniques helped to obtain some “useful” information.

“It is our considered view that the detainees who were subjected to enhanced interrogation techniques provided information that was useful and was used in the ultimate operation to go against Bin Laden,” Mr Brennan said.

— with AAP