A federal appeals court in Manhattan Monday ordered the Obama administration to disclose the official legal justification for the drone strike that killed alleged al-Qaida operative Anwar al-Awlaki, an American citizen, in 2011.

Although the Justice Department argued releasing the memo from its Office of Legal Counsel could inhibit internal discussions and reveal classified information, the Second Circuit Court of Appeals said the government had already let the cat out of the bag by answering critics and issuing a "white paper."

"After senior Government officials have assured the public that targeted killings are 'lawful' and that OLC advice 'establishes the legal boundaries within which we can operate,' and the Government makes public a detailed analysis, waiver of secrecy and privilege . . . has occurred," said a three-judge panel.

The ruling came in a Freedom of Information Act lawsuit by the American Civil Liberties Union and The New York Times. The court said much of its opinion and the legal memo itself would remain under wraps until the government decides on an appeal.

Awlaki was killed along with his son and another man, both also American citizens, in the drone strike in Yemen. The United States said he was involved in motivating and planning attacks on American targets.

In a 2012 speech, Attorney General Eric Holder said killing Americans with drone strikes complied with the constitutional guarantee of "due process" as long as a "thorough and careful" government review indicated the person was an imminent threat and capture wasn't "feasible."

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Later, a "white paper" outlining the legal reasoning was leaked to the media and then officially released. But the government continued to resist requests for the official and more detailed Justice Department legal analysis, which the court said ran 41 pages.

"Whatever protection the legal analysis might once have had has been lost by virtue of public statements of public officials at the highest levels and official disclosure of the DOJ White Paper," the appeals court panel said in its 52-page decision.

The Justice Department had no comment on the ruling or on any plans to appeal. The suit sought only the release of the legal analysis behind the drone program, and did not challenge the legality of the program.

Jameel Jaffer, the lead ACLU lawyer on the case, called the ruling a "resounding rejection of the government's effort to use secrecy and selective disclosure to manipulate public opinion about the targeted killing program."

"The government can't legitimately claim that everything about the targeted killing program is a classified secret while senior officials selectively disclose information meant to paint the program in the most favorable light," Jaffer said in a statement.