The 15 boxes of White House records that were stored at former president Donald Trump’s Mar-a-Lago residence contained items marked as classified national security information, the National Archives and Records Administration said on Friday.
The agency said the matter has been referred to the Justice Department.
In a response to a February 9 letter to the House Committee on Oversight and Reform, the National Archives confirmed reports that Mr Trump took government records with him to Florida after he left office in January 2021.
Members of the House of Representatives have opened an investigation and the National Archives has reportedly asked the Justice Department to look into the matter. The Justice Department and the FBI have not yet disclosed what they intend to do.
Mr Trump was unwilling to part with some of his administration’s records when he left the White House last year.
Although more than a dozen boxes have since been returned to the government, the discovery alarmed archivists and historians who were already sceptical of Mr Trump’s commitment to transparency.
The Presidential Records Act, which requires the preservation of White House documents, was passed in 1978 after the Watergate scandal, when a collection of secret tapes played a defining role.
Official records can still prove insightful once they become public, after being processed by the National Archives, which can take years.
Mr Trump last week denied as "fake" claims that he flushed presidential documents down the toilet at the White House.
The New York Times's Maggie Haberman, author of coming book on Mr Trump called The Confidence Man, said in a tweet: “White House residence staff periodically found papers had clogged a toilet, leaving staff believing Mr Trump had flushed material he'd ripped into pieces.”
Mr Trump’s erratic handling of documents could have more immediate effects than the eventual judgment of historians. The congressional committee investigating the January 6, 2021, attack on the US Capitol is examining the former president’s actions that day, but finding gaps in official records such as call logs.
There’s also the potential for legal trouble if Mr Trump or his associates are determined to have mishandled any documents, especially if they’re classified. Presidents have the power to declassify any information they choose, but that expires after they leave office.
Concealing or destroying records is a crime carrying a prison term of up to three years; storing classified information in an unauthorised location can carry a sentence of up to five years.
Associated Press contributed to this report
