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.