The Obama administration acknowledged publicly for the first time that four U.S. citizens have been killed in drone strikes since 2009 in Pakistan and Yemen. The disclosure comes on the eve of a major national security speech by President Barack Obama in which he plans to pledge more transparency to Congress in his counterterrorism policy.

The White House said Mr. Obama’s speech on Thursday coincides with the signing of new “presidential policy guidance” on when the U.S. can use drone strikes, though it was unclear what that guidance entailed and whether Mr. Obama would outline its specifics in his remarks.

A move to gradually shift responsibility for the bulk of U.S. drone strikes from the CIA to the military has already begun. The CIA would continue to conduct operations in Pakistan, while the military takes on the operations in other parts of the world, according to an administration official.

It was already known that three Americans had been killed in U.S. drones strikes in counterterrorism operations overseas, but the government’s top lawyer, Attorney General Eric Holder, disclosed details that had remained secret, including the fourth citizen killed.

In a letter to the chairman of the Senate Judiciary Committee, Mr. Holder said the government targeted and killed U.S. citizen Anwar al-Awlaki, a radical cleric, in Yemen.

The other two known cases have been: Samir Khan, killed in the same drone strike as Awlaki; and Awlaki’s son, Abdulrahman (16), also killed in Yemen.

The newly revealed case is that of Jude Kenan Mohammad, one of eight men indicted by federal authorities in 2009 in a plot to attack the U.S. Marine Corps base at Quantico, Virginia, and who fled to Pakistan.

— AP