WASHINGTON – A secret U.S. military investigation in 2010 determined that Michael 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.

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.

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

The office of the Army’s Judge Advocate General released a four-page summary of the investigation into Flynn in response to a request by the Washington Post. The documents provide the first official account of the case, but the investigation itself remains classified.

The U.S. military opened the investigation into Flynn in 2010 after receiving a complaint from an unnamed Navy intelligence specialist, according to the documents. The intelligence officer charged that Flynn violated rules by "inappropriately" sharing secrets with "various foreign military officers and/or officials in Afghanistan."

The documents do not reveal the nature of the information. But former U.S. officials familiar with the case said it centered on slides and other materials containing classified information about CIA operations in Afghanistan.

"It was a general intelligence briefing that included stuff that shouldn’t have been on those slides," said a former senior U.S. intelligence official, who, like others, spoke on the condition of anonymity, citing the sensitivity of the subject. The disclosures revealed "stuff the intelligence community was doing that had a much higher level of classification."

The newly disclosed Army documents state that the 2010 investigation was ordered by the head of U.S. Central Command, which oversees military operations in the Middle East and Afghanistan.

Although the records do not say exactly when the case was opened, the commander at the time would have been Marine Gen. James Mattis, who took charge at Central Command’s headquarters in Tampa, Florida, in August 2010. One month later, Flynn was ordered back to Washington from Afghanistan while the investigation unfolded, records show.

Mattis was nominated this month by Trump to serve as secretary of defense. In that role, Mattis will work closely with Flynn; the retired generals are expected to be the most influential voices on national security in the Trump administration.

The episode marked the second time in a year that Flynn had drawn official complaints for his handling of classified material. Former U.S. officials said that Flynn had disclosed sensitive information to Pakistan in late 2009 or early 2010 about secret U.S. intelligence capabilities being used to monitor the Haqqani network, an insurgent group accused of repeated attacks on U.S. forces in Afghanistan.

During the presidential race, Flynn drew attention for his scalding attacks against Democratic opponent Hillary Clinton for mishandling classified material.