The U.S. government has issued an unclassified Justice Department memo that authorizes the killing of American citizens as part of its controversial drone campaign against al-Qaeda, even without the intelligence that the Americans have plans to attack a U.S. target, Reuters reported.

According to the memo, first obtained by NBC News, if a targeted U.S. citizen had "recently" been involved in "activities" posing a possible threat, and there is no evidence that the person "renounced or abandoned" these activities, a drone strike would be authorized, Reuters reported.

The document was released after a bipartisan group of senators asked the Obama administration to explain to Congress "any and all" legal opinions outlining the legal powers the president has to purposefully kill American citizens, Reuters reported.

One national security official told Reuters that the said the leak of the Justice Department document may have been timed, in order to halt congressional demands for more, possibly classified, documents relating to the U.S. use of drones.

Senator Deanne Feinstein, the Democratic chair of the Senate intelligence committee, told Reuters that she had been waiting for over a year for the administration to release legal analyses about the use of drones.

The document released to NBC, Feinstein told Reuters, had been provided to congressional committees on a confidential basis last June, but her committee is seeking additional, possibly classified, documents.

According to the document, in order for a person to be targeted, he or she must pose "an imminent threat of violent attack against the United States," cannot be captured, and the strike "would be conducted in a manner consistent with applicable law of war principles," Reuters reported.

The document calls attention to one of the Obama administration's controversial drone programs, which has killed Al-Qaeda suspects, including American citizens, abroad. One notable incident was the Sept. 2011 drone strike in Yemen, where al-Qaeda operatives Anwar al-Awlaki and Samir Khan, both U.S. citizens, were killed, despite never having been charged with crimes by the U.S. government.

Hina Shamsi, head of The American Civil Liberties Union, called the document a "profoundly disturbing" and "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," according to The Washington Post.

Shamsi also asked the Obama administration to release what she said is a 50-page document on which the 16-page memo was based.

"Among other things, we need to know if the limits the executive purports to impose on its killing authority are as loosely defined as in this summary, because if they are, they ultimately mean little," she told Reuters.