WASHINGTON (CNN) -- A Justice Department memo determined the U.S. government can use lethal force against an American citizen overseas if the person is a senior operational leader of al Qaeda or one of its affiliates, according to a document posted on the NBC News website.
The paper provides insights into the Obama administration's policy of targeted killings carried out by the use of drone strikes against suspected terrorists. Several of those strikes have killed Americans, notably Anwar al-Awlaki, the Yemeni American who had been connected to plots against the United States but never charged with a crime. Awlaki died in a drone attack in September 2011 in Yemen.
The 16-page white paper -- titled "Lawfulness of a Lethal Operation Directed Against a U.S. Citizen who is a Senior Operational Leader of Al Qaida or an Associated Force" -- is a policy paper rather than an official legal document.
According to NBC, the confidential Justice Department memo was given to members of the Senate Intelligence and Judiciary committees by the administration last June.
The paper states that although U.S. citizens abroad retain their constitutional rights to due process, the U.S. government can use lethal force against a citizen under the following circumstances: "1) where an informed, high-level official of the U.S. government has determined that the targeted individual poses an imminent threat of violent attack against the United States; 2) where a capture operation would be infeasible -- and where those conducting the operation continue to monitor whether capture becomes feasible; and 3) where such an operation would be conducted consistent with applicable law of war principles."
But the document also says the government is not required "to have clear evidence" that an attack against the United States will occur in the immediate future to determine that an imminent threat is posed by a U.S. citizen.
The memo cites both congressional authorization and judicial approval for the use of military force to counter the threat of terrorist attack by all individuals.
The Supreme Court has held that the military may constitutionally use force against a U.S. citizen who is a part of enemy forces.
The document dismisses arguments by commentators that the war against al Qaeda cannot extend outside of Afghanistan, and asserts, "the United States retains its authority to use force against al-Qaida and associated forces outside the area of active hostilities when it targets a senior operational leader of the enemy force who is actively engaged in planning operations to kill Americans."
The American Civil Liberties Union called the document "profoundly disturbing."
Hina Shamsi, the director of the ACLU's National Security Project, said, "It summarizes in cold legal terms a stunning overreach of executive authority, the claimed power to declare Americans a threat and kill them far from a recognized battlefield and without any judicial involvement before or after the fact."
Shamsi called on the Obama administration to release the 50-page legal memo on which the White Paper is based.
A bipartisan group of senators has also called for the administration to release its legal opinions on presidential authority.
In a letter to the president on Monday, the 11 senators said, "It is vitally important, however, for the Congress and the American public to have a full understanding of how the executive branch interprets the limits and boundaries of this authority so that Congress and the public can decide whether this authority has been properly defined and whether the president's power to deliberately kill American citizens is subject to appropriate limitations and safeguards."
The letter is signed by Sens. Ron Wyden, D-Oregon, Mark Udall, D-Colorado, and Susan Collins, R-Maine, of the Intelligence Committee as well as Mike Lee, R-Utah; Chuck Grassley, R-Iowa; Jeff Merkley, D-Oregon; Dick Durbin, D-Illinois; Patrick Leahy, D-Vermont; Tom Udall, D-New Mexico; Mark Begich, D-Alaska; and Al Franken, D-Minnesota.
The request comes just days before the confirmation hearing of John Brennan to become director of the CIA. Brennan, who has served as the president's top counterterrorism adviser, is considered to be behind the administration's dramatic rise in the use of targeted killings.
He is expected to be grilled on the policy during his hearing Thursday.