Citing the Privacy Act, the CIA would not provide any details about the officer's identity or assignments. It was not immediately clear if the person would face prosecution. The firing is a highly unusual move, although there has been an ongoing investigation into leaks in the CIA.
"The officer has acknowledged unauthorized discussions with the media and the unauthorized sharing of classified information," said CIA spokesman Paul Gimigliano. "That is a violation of the secrecy agreement that everyone signs as a condition of employment with the CIA."
One official called this a "damaging leak" that deals with operational information and said the fired officer "knowingly and willfully" leaked the information to the media and "was caught."
The CIA officer was not in the public affairs office, nor was he someone authorized to talk to the media. The investigation was launched in January by the CIA's security center. It was directed to look at employees who had been exposed to certain intelligence programs. In the course of the investigation, the fired officer admitted discussing classified information including information about classified operations.
A senior law enforcement official said the person fired failed a polygraph test, which was given as part of the agency's internal investigation into media leaks. As to which or how many questions the person failed, the official said they didn't know.
On the subject of potential prosecution, the official said if the person admitted to leaking classified information, it would be almost negligent not to prosecute them for breaking the law. Failing a polygraph in and of itself does not qualify a person for prosecution but an admission does.
The investigation is ongoing.
A Justice Department spokesman said "no comment" on the firing. The spokesman also would not say whether the agency was looking into any criminal action against the officer. One law enforcement official said there were dozens of leak investigations under way.
A second law enforcement official confirmed said the CIA officer had provided information that contributed to a Washington Post story last year saying there were secret U.S. prisons in Eastern Europe.
Sources have told FOX News in the past that the CIA prisons/black sites story was referred to the Justice Department for investigation. That story involved the transfer of terror suspects to other countries for questioning. Some believe the CIA transferred suspects to secret prisons in countries where torture is more acceptable; secret prisons and many harsh methods of interrogation would be illegal on U.S. soil.
The administration has refused to address the question of whether it operated such secret sites that may be illegal under European law, citing the constraints of classified information.
The Washington Post report caused an international uproar, and government officials have said it did significant damage to relationships between the U.S. and allied intelligence agencies.
CIA Director Porter Goss has pressed for aggressive investigations. In his latest appearance before Congress, Goss condemned the unauthorized disclosure of information.
"The damage has been very severe to our capabilities to carry out our mission," Goss said in February, adding that a federal grand jury should be impaneled to determine "who is leaking this information."
FOX News' Bret Baier, Wendell Goler and Mike Levine and The Associated Press contributed to this report.