Federal investigators are conducting a probe into who leaked information about an Al Qaeda plot in which an explosive device was to have been detonated on a U.S.-bound airline flight, a law enforcement official said Wednesday.

The official spoke on condition of anonymity about the leak investigation, which is just getting under way.

The federal investigation is the latest move in an aggressive campaign by the Obama administration to crack down on leaks, even as it has supported proposed legislation that would shield reporters from having to identify their sources. The probe would represent at least the seventh criminal leak case opened under the Obama administration, more than were opened under any previous presidency.

The investigation follows stories by The Associated Press and other news organizations disclosing the terrorist operation by the group known as Al Qaeda in the Arabian Peninsula.

The reports said that Al Qaeda had completed a sophisticated new, nonmetallic underwear bomb last month and that the would-be suicide bomber actually was a double agent working with the CIA and Saudi intelligence agencies.

The would-be suicide bomber secretly turned over the group's most up-to-date underwear bomb to Saudi Arabia, which gave it to the CIA. Before he was whisked to safety, the spy provided intelligence that helped the CIA kill Al Qaeda's senior operations leader, Fahd al-Quso, who died in a drone strike last weekend.

In an appearance Wednesday before the House Judiciary Committee, FBI Director Robert Mueller said the FBI is examining the explosive device. He said the scheme hatched in Yemen demonstrates that it's essential for Congress to reauthorize counterterrorism tools enacted in 2008. Some of these programs expire at year's end.

A spokesman for the AP, Paul Colford, said in a statement that the news organization "acted carefully and with extreme deliberation in its reporting on the underwear bomb plot and its subsequent decision to publish."

"As the AP has reported, we distributed our exclusive report on the underwear bomb only after officials assured us -- on Monday -- that their security concerns had been satisfied and we learned that the White House would announce the news the next day," Colford said.