WASHINGTON - 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.

But Brennan asserted the CIA "did a lot of things right" in a time when there were "no easy answers, saying that CIA officers were acting under Bush administration guidance that harsh techniques were legal.

The CIA was brought to sharper focus following the release Tuesday of a Senate Intelligence Committee report, in which details were offered about CIA's brutal interrogation methods over the years after the Sept. 11, 2001 terrorist attacks on the U.S. mainland.

Among the methods were waterboarding, sexual threats and sleep deprivation, though the report found the techniques largely ineffective and poorly managed.

The revelations have sparked outrage and demands for justice around the world.