Attorney General Eric Holder said on Thursday that President Barack Obama would not have the authority to order a drone to kill an American citizen on U.S. soil who was "not engaged in combat."
In a two-sentence letter to Kentucky Republican Senator Rand Paul, Holder said he had heard Paul wanted to know if the president could use a drone to kill an American outside of an emergency situation.
"The answer to that question is no," Holder wrote.
He was responding in part to Paul's extensive critique of a letter the attorney general sent to the senator, which was made public on Tuesday. Holder said then that drone strikes against Americans on U.S. soil were not anticipated, but he did not rule them out in circumstances similar to the September 11 attacks in 2001.
On Wednesday, Paul spent nearly 13 hours speaking on the Senate floor in an attempt to block the confirmation of John Brennan as the next CIA director in protest at the use of drones in targeted killings.
The Obama administration has increasingly used drone strikes to target militants overseas, particularly in Pakistan and Yemen.