United States justice officials say they have opened a formal criminal investigation of leaks to the media of classified material on national security.
US Attorney-General Eric Holder named two lawyers to lead the criminal investigations into "possible unauthorised disclosures" of classified information.
The announcement was made hours after President Barack Obama rejected allegations from some members of Congress that his White House had leaked information for political gain and had jeopardised national security.
The New York Times reported last week that President Obama personally ordered drone attacks targeting terrorists on a "kill list" and that he ordered a series of Stuxnet computer worm attacks against Iran's alleged nuclear weapons program.
An additional leak in May revealed that an al-Qaeda plot to bomb a US-bound airliner was disrupted with the help of a Saudi double agent inside the terrorist network in Yemen.
Mr Obama said on Friday he would not "play" with security issues and said he would root out those responsible for the disclosures.