The U.S. has killed four American citizens in drone attacks, Attorney General Eric Holder told lawmakers in a letter made public Wednesday.

The letter comes the day before President Obama is slated to lay out his administration’s legal justification for using drones against terrorists in a speech at the National Defense University.

Holder’s letter states that the four Americans were killed in counterterrorism operations and does not use the word drones.

It states that Anwar al-Awlaki, an American-born Muslim cleric, was targeted by the U.S. It has been widely reported that al-Awlaki was killed in a 2011 drone attack in Yemen.

The letter mentions that the U.S. is aware of “three other U.S. citizens who have been killed in such counterterrorism operations over that same time period.”