The Obama administration acknowledged publicly for the first time that four US 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 Obama's speech today coincides with the signing of new "presidential policy guidance" on when the US can use drone strikes, though it was unclear what that guidance entailed and whether Obama would outline its specifics in his remarks.
A move to gradually shift responsibility for the bulk of US 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 speaking on condition of anonymity because he wasn't authorised to speak publicly,.
It was already known that three Americans had been killed in US 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, Holder said the government targeted and killed US citizen Anwar al-Awlaki and that the US "is aware" of the killing of three others who were not targets of counterterror operations.
Al-Awlaki, a radical Muslim cleric, was killed in a drone strike in September 2011 in Yemen. The other two known cases have been Samir Khan, who was killed in the same drone strike as al-Awlaki and al-Awlaki's 16-year-old son, Abdulrahman, who also was killed in Yemen.
The newly revealed case is that of Jude Kenan Mohammed, one of eight men indicted by federal authorities in 2009 and accused of being part of a plot to attack the US Marine Corps base at Quantico, Virginia. Before he could be arrested, Mohammad fled the country to join jihadi fighters in the tribal areas of Pakistan, where he was among those killed by a US drone.
"Since entering office, the president has made clear his commitment to providing Congress and the American people with as much information as possible about our sensitive counterterrorism operations," Holder said in his letter. "To this end, the president has directed me to disclose certain information that until now has been properly classified."
Obama's speech is expected to reaffirm his national security priorities — from homegrown terrorists to killer drones to the enemy combatants imprisoned at Guantanamo Bay — but make no new sweeping policy pronouncements.
Obama is expected to say the US will make a renewed effort to transfer detainees out of the Navy-run detention centre for terrorist suspects at Guantanamo Bay, Cuba, to other countries. Obama recently restated his desire to close Guantanamo, a pledge he made shortly after his inauguration in January 2009.
That effort, however, has been stymied because many countries don't want the detainees or are unwilling or unable to guarantee that once transferred, detainees who may continue to be a threat will not be released.
There are currently about 166 prisoners at Guantanamo, and 86 have been approved for transfer as long as security restrictions are met.
Obama is also expected to make the case that the US-led war in Afghanistan has decimated al-Qa'ida's core, even as new threats emerge elsewhere.