WASHINGTON — A secret U.S. military investigation in 2010 determined that Michael T. Flynn, the retired Army general tapped to serve as national security adviser in the Trump White House, “inappropriately shared” classified information with foreign military officers in Afghanistan, newly released documents show.

Although Flynn lacked authorization to share the classified material, he was not disciplined or reprimanded after the investigation concluded that he did not act “knowingly” and that “there was no actual or potential damage to national security as a result,” according to Army records obtained by The Washington Post under the Freedom of Information Act.

Flynn has previously acknowledged that he was investigated while serving as the U.S. military intelligence chief in Afghanistan for sharing secrets with British and Australian allies there. But he has dismissed the case as insignificant and has given few details.

The Army documents provide the first official account of the case, but they are limited in scope because the investigation itself remains classified. Former U.S. officials familiar with the matter said that Flynn was accused of telling allies about the activities of other agencies in Afghanistan, including the CIA.

The Army files call into question Flynn’s prior assertion that he had permission to share the sensitive information.

During the presidential race, Flynn campaigned vigorously for Republican nominee Donald Trump and drew attention for his scalding attacks against Democratic opponent Hillary Clinton for mishandling classified material. Clinton was investigated by the FBI for allowing classified information to be transmitted on her private email server when she ran the State Department. No charges were filed against the former secretary of state, but the issue dogged her for more than a year.

At the Republican National Convention in July, Flynn called on Clinton to drop out of the race for putting “our nation’s security at extremely high risk with her careless use of a private email server.” He egged on the partisan crowd in chants of “lock her up,” adding: “If I, a guy who knows this business, if I did a tenth, a tenth of what she did, I would be in jail today.”

Flynn did not respond to requests for comment.

The office of the Army’s Judge Advocate General released a four-page summary of the investigation into Flynn in response to The Post’s Freedom of Information Act request for records of any misconduct allegations involving the retired three-star general.