Washington (CNN) -- Counterterrorism drone strikes have killed four Americans overseas since 2009, the U.S. government acknowledged for the first time on Wednesday, one day before President Barack Obama delivers a major speech on related policy.
In a letter to Senate Judiciary Committee Chairman Patrick Leahy, Attorney General Eric Holder said the United States specifically targeted and killed one American citizen, al Qaeda cleric Anwar al-Awlaki, in 2011 in Yemen, alleging he was plotting attacks against the United States.
The letter provided new details about al-Awlaki's alleged involvement in bomb plots targeting U.S. aviation.
Holder also said the Obama administration was aware of three other Americans who had been killed in counterterrorism operations overseas.
Holder said Samir Kahn, Abdul Rahman Anwar al-Awlaki and Jude Kenan Mohammed were not targeted by the United States but he did not add more details about their deaths.
The letter represents the first U.S. admission that the four were killed in counterterror strikes even though their deaths had been reported in the media.
Abdul Rahman Anwar Al-Awlaki was the 16-year-old son of the al Qaeda cleric and was killed in Pakistan about two weeks after his father's death.
Khan produced the English-language magazine Inspire for al Qaeda's affiliate in the Arabian Peninsula, which included bomb-making instruction. He was killed alongside the elder al-Awlaki.
Mohammed, who was once on the FBI's Most Wanted list, was indicted in July 2009 as part of a North Carolina-based terror ring. He was charged with plotting to murder, kidnap or maim persons overseas and provide material support to terrorists. Mohammed was never arrested and for a time reportedly was living in Pakistan.
The Justice Department did not say when he was killed or provide any details.
Obama will deliver long-promised remarks on Thursday at National Defense University and will speak at length about the policy and legal rationale for how the United States takes action against al Qaeda and its affiliates, including the use of drones, according to a White House official.
Obama will discuss the administration's rationale for why those strikes are legal and necessary, the official said.
Targeting Americans with lethal force in counterterror operations overseas was a controversy that flared publicly during confirmation hearings for CIA Director John Brennan earlier this year.
Senators aggressively sought the administration's legal reasoning for those operations.
Some lawmakers were critical of the practice and questions were raised about whether drones might ever be used against U.S. citizens suspected of terrorism who were on American soil.
Holder said Obama directed him to release the latest details, which had been classified "until now." He said the unprecedented disclosure was made as a way to build on Obama's commitment in his State of the Union Address earlier this year to "continue to engage" with Congress on counterterror efforts and to "ensure that they remain consistent with our laws and values."
Holder noted in one of his own speeches last year he had made it clear the United States would only use lethal force against an American citizen "who is a senior operational leader of al Qaeda or its associated forces, and who is actively engaged in planning to kill Americans." He also said no American would be targeted unless he or she posed an imminent threat and could not be captured.
The senior al-Awlaki was believed by U.S. authorities to have inspired acts of terrorism against the United States. It was said his facility with English and technology made him one of the top terrorist recruiters in the world. He was considered the public face of al Qaeda in the Arabian Peninsula.
But Holder said in his letter that it "was not his words that led the United States to act against him" but his "direct personal involvement" in the "planning and execution" of terror attacks against the United States that "made him a lawful target."
For instance, Holder said al-Awlaki "planned a suicide operation" for Umar Farouk Abdulmutallab to blow up a U.S.-bound jetliner.
Holder noted al-Awlaki directed Abdulmutallab to detonate his bomb, which was hidden in his underwear, only when the jet was over U.S. soil. The plot that ultimately involved a Delta Air Lines flight bound for Detroit on Christmas Day in 2009 failed.
The letter also provided new details about al-Awlaki's alleged involvement in a 2010 plot to blow up U.S.-bound cargo planes with explosives hidden in printers. Holder said al-Awlaki was so involved he even participated in the development and testing of the explosives used in the plan that was foiled.
Calling the decision to use lethal force "one of the gravest our government" can face," Holder said the operation targeting al-Awlaki received "exceptionally rigorous" legal review and additional policy screening by the administration. Congress was also briefed on the possibility of targeting the al Qaeda figure and informed once the decision was made in 2010.
In his letter Holder said Obama approved a policy document this week that "institutionalizes the administration's exacting standards and processes for reviewing and approving operations to capture or use lethal force against terrorist targets outside the United States and areas of active hostilities."
Obama focuses on drones, Gitmo
CNN's Jessica Yellin contributed to this report.