Former US president Donald Trump took classified information to his Florida home after leaving the White House, the national archivist says.
The US National Archives and Records Administration (NARA) revealed the details in a letter to Congress about 15 boxes of documents it recently recovered from Mr Trump's Mar-a-Lago residence.
The letter said National Archives informed the Department of Justice, which would handle any investigation.
"NARA has identified items marked as classified national security information within the boxes," David Ferriero, the archivist of the United States, said in a letter to Democratic congresswoman Carolyn Maloney, chair of the House of Representatives oversight committee.
Ms Maloney's committee has been looking into Mr Trump's handling of records by the Republican president, who left office in January 2021.
US politicians are also seeking information about the contents of the boxes recovered from Mar-a-Lago but the National Archives cited the records act as holding them back from divulging.
A spokesman for Mr Trump did not immediately respond to a request for comment.
But Mr Trump recently denied reports about his administration's tenuous relationship with the National Archives and his lawyers said "they are continuing to search for additional presidential records that belong to the National Archives".
Electronic messages and social media records not captured
The letter from Mr Ferriero said some White House staff conducted official business using non-official electronic messaging accounts that were not copied or forwarded into official electronic messaging accounts and that it was in the process of obtaining some of those missing records.
The letter details how certain social media records were not captured and preserved by Mr Trump's administration.
The Presidential Records Act requires the preservation of memos, letters, notes, emails, faxes and other written communications related to a president's official duties.
Claiming executive privilege, Mr Trump unsuccessfully attempted to sue to stop the release of records from his White House, including to the House select committee investigating the January 6, 2021 attack on the US Capitol.
ABC/wires
