A federal appeals panel in Manhattan ordered the release on Monday of key portions of a classified Justice Department memorandum that provided the legal justification for the targeted killing of a United States citizen, Anwar al-Awlaki, who intelligence officials contend had joined Al Qaeda and died in a 2011 drone strike in Yemen.

The unanimous three-judge panel, reversing a lower court decision, said the government had waived its right to keep the analysis secret in light of numerous public statements by administration officials and the Justice Department’s release of a “white paper” offering a detailed analysis of why targeted killings were legal.

“Whatever protection the legal analysis might once have had,” Judge Jon O. Newman wrote for the panel of the United States Court of Appeals for the Second Circuit, “has been lost by virtue of public statements of public officials at the highest levels and official disclosure of the D.O.J. White Paper.”

The ruling stemmed from lawsuits filed under the Freedom of Information Act by The New York Times and two of its reporters, Charlie Savage and Scott Shane, and by the American Civil Liberties Union.