Correction: An earlier version of this article misstated the circumstances of another U.S. drone attack in Yemen, in 2002. The article indicated that a U.S. citizen killed in an attack targeting al-Qaeda operative Abu Ali al-Harithi was also a target. The CIA knew the second man was in Harithi’s vehicle, but he was not a target. This version has been updated.

The Justice Department wrote a secret memorandum authorizing the lethal targeting of Anwar al-Aulaqi, the American-born radical cleric who was killed by a U.S. drone strike Friday, according to administration officials.

The document was produced following a review of the legal issues raised by striking a U.S. citizen and involved senior lawyers from across the administration. There was no dissent about the legality of killing Aulaqi, the officials said.

“What constitutes due process in this case is a due process in war,” said one of the officials, who spoke on the condition of anonymity to discuss closely held deliberations within the administration.

The administration has faced a legal challenge and public criticism for targeting Aulaqi, who was born in New Mexico, because of constitutional protections afforded U.S. citizens. The memorandum may represent an attempt to resolve, at least internally, a legal debate over whether a president can order the killing of U.S. citizens overseas as a counterterrorism measure.

The operation to kill Aulaqi involved CIA and military assets under CIA control. A former senior intelligence official said that the CIA would not have killed an American without such a written opinion.

A second American killed in Friday’s attack was Samir Khan, a driving force behind Inspire, the English-language magazine produced by al-Qaeda in the Arabian Peninsula. An administration official said the CIA did not know Khan was with Aulaqi, but they also considered Khan a belligerent whose presence near the target would not have stopped the attack.

The circumstances of Khan’s death were reminiscent of a 2002 U.S. drone strike in Yemen that targeted Abu Ali al-Harithi, a Yemeni al-Qaeda operative accused of planning the 2000 attack on the USS Cole. That strike also killed a U.S. citizen who the CIA knew was in Harithi’s vehicle but who was not a target of the attack.

The Obama administration has spoken in broad terms about its authority to use military and paramilitary force against al-Qaeda and associated forces beyond “hot,” or traditional, battlefields such as Iraq or Afghanistan. Officials said that certain belligerents aren’t shielded because of their citizenship.

“As a general matter, it would be entirely lawful for the United States to target high-level leaders of enemy forces, regardless of their nationality, who are plotting to kill Americans both under the authority provided by Congress in its use of military force in the armed conflict with al-Qaeda, the Taliban, and associated forces as well as established international law that recognizes our right of self-defense,” an administration official said in a statement Friday.

President Obama and various administration officials referred to Aulaqi publicly for the first time Friday as the “external operations” chief for al-Qaeda in the Arabian Peninsula, a label that may be intended to underscore his status as an operational leader who posed an imminent threat.

A Justice Department spokeswoman declined to comment. The administration officials refused to disclose the exact legal analysis used to authorize targeting Aulaqi, or how they considered any Fifth Amendment right to due process.

Robert Chesney, a law professor at the University of Texas at Austin who specializes in national security law, said the government likely reviewed Aulaqi’s constitutional rights, but concluded that he was an imminent threat and was deliberately hiding in a place where neither the United States nor Yemen could realistically capture him.

Last year, the Obama administration invoked the state secrets privilege to argue successfully for the dismissal of a lawsuit brought in U.S. District Court in Washington by Aulaqi’s father, Nasser, seeking to block the targeting of his son. Judge John Bates found that in Aulaqi’s case, targeting was a “political question” to be decided by the executive branch.

The decision to place Aulaqi on a capture or kill list was made in early 2010, after intelligence officials concluded that he played a direct role in the plot to blow up a jet over Detroit and had become an operational figure within al-Qaeda’s affiliate in Yemen.

“If you are a dual national high in the Japanese operational group responsible for Pearl Harbor, you’re not exempt, and neither was” Aulaqi, the administration official said.

The American Civil Liberties Union and the Center for Constitutional Rights argued on behalf of Aulaqi’s father last year that there is no “battlefield” in Yemen and that the administration should be forced to articulate publicly its legal standards for killing any citizen outside the United States who is suspected of terrorism.

Otherwise, the groups argued, such a killing would amount to an extrajudicial execution and would violate U.S. and international law.

“International human rights law dictates that you can’t unilaterally target someone and kill someone without that person posing an imminent threat to security interests,” said Vince Warren, executive director of the Center for Constitutional Rights. “The information that we have, from the government’s own press releases, is that he is somehow loosely connected, but there is no specific evidence of things he actualized that would meet the legal threshold for making this killing justifiable as a matter of human rights law.”

ACLU lawyer Ben Wizner said that Aulaqi had been targeted for nearly two years and that the government would appear to have a very elastic definition of imminent threat.

The former senior intelligence official said the CIA did reviews every six months to ensure that those targeted for possible killing remained threats as defined by law and presidential findings.

The administration describes al-Qaeda in the Arabian Peninsula as an associated force of the original terrorist group that was led by Osama bin Laden until he was killed, making AQAP subject to congressionally authorized military force. Officials said Aulaqi was part of an enemy force and posed an ongoing, immediate danger.

Staff writer Mary Beth Sheridan and staff researcher Julie Tate contributed to this report.