WASHINGTON, Dec. 11 (Xinhua) -- The chief of the Central Intelligence Agency (CIA) conceded Thursday that there was no proof of useful information yielded from the brutal interrogation techniques used by the agency on terrorism detainees.

John Brennan, in a rare televised press conference held at the CIA headquarters in Langley, Virginia, acknowledged "unauthorized" and "abhorrent" practices by some officers, saying it was " unknowable" whether the so-called enhanced interrogation techniques produced key intelligence.

"We fell short when it came to holding some officers accountable for their mistakes," he said, adding that the use of coercive methods has a strong prospect for resulting in false information because "if somebody is being subjected to a course of techniques, they say something to have those techniques stopped".

"And so there have been a lot of studies done over the years about the value of different types of interrogation methods and whether or not coercive methods can lead to useful information that couldn't otherwise obtained," the CIA chief noted.