NBC News has published a leaked document outlining the legal basis the Obama administration used to kill American citizens in Yemen. The Justice Department memo states that the United States can order the killing of U.S. citizens if the person is a “senior operational leader” in Al Qaeda–”even if there is no intelligence indicating they are engaged in an active plot to attack the U.S,” NBC News’ Michael Isikoff reports.

The memo provides the legal reasoning behind the U.S.-ordered drone attacks on Anwar al-Awlaki, the Yemeni cleric who was a U.S. citizen. No charges were ever filed against Awlaki before he was assassinated. His 16-year-old son, Abdulrahman al-Awlaki, was also killed in a separate strike by the U.S.

The memo will do little to quell the controversy over the Obama administration’s targeted killings program and use of drone strikes to kill U.S. citizens. As Isikoff reports, “the confidential Justice Department ‘white paper’ introduces [an] expansive definition of self-defense or imminent attack.”

“The condition that an operational leader present an ‘imminent’ threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future,” the paper states.

The memo says that an “informed, high level” official can make the determination as to whether it is lawful to carry out an attack on an American citizen. An attack can be carried out if the American “has been ‘recently’ involved in ‘activities’ posing a threat of a violent attack and ‘there is no evidence suggesting that he has renounced or abandoned such activities,’” NBC News reports.

The paper reportedly is a summary of the official legal document prepared by the Justice Department’s Office of Legal Counsel that outlines why the Obama administration had the authority to kill Awlaki. Senators have been pushing the Obama administration to release the official memo justifying the killing of Americans, and the issue is sure to come up Thursday during the confirmation hearings for John Brennan. Brennan, the architect of the drone policy, is slated to head the CIA if he is confirmed.

The paper lays out three parts that determine how the killing of an American is lawful. It states that the suspect must be an “imminent” threat; that the capture of the target must beunfeasible; and that the strike must comport with “law of war” principles.

But the U.S. government’s definition of an “imminent” threat has come under fire from the American Civil Liberties Union.

“The paper initially suggests, for example, that the government's authority to use lethal force is limited to people who present ‘imminent’ threats, but it then proceeds to redefine the word imminence in a way that deprives the word of its ordinary meaning,” wrote Jameel Jaffer of the ACLU. “The paper does something similar with the phrase ‘capture is infeasible.’ It initially sounds like a real limitation but by page 8 it seems to mean only that the government won't use lethal force if capture is more convenient. It's the language of limits—but without any real restrictions.”