A document describing a foreign government’s military defences, including its nuclear capabilities, was reportedly found in the FBI’s search of former President Donald Trump’s Florida home last month.
The Washington Post, which cited people close to the matter, reported the discovery during the raid but has not identified the foreign government discussed in the document.
It also did not indicate whether the foreign government was friendly or hostile to the United States.
An FBI spokesperson declined to comment on the report.
Mr Trump’s representatives did not immediately respond to requests for comment.
The FBI recovered more than 11,000 government documents and photographs during its 8 August search at Mr Trump’s Mar-a-Lago estate, according to court records.
According to the Post report, some of the seized documents detail top-secret US operations that require special clearances, not just top-secret clearance.
Some of the documents are so restricted that even some of the Biden administration’s senior-most national security officials were not authorised to review them, the Post said.
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The US Justice Department is investigating Trump for removing government records from the White House after he departed in January 2021 and storing them at Mar-a-Lago.
On Monday, a federal judge agreed to Trump’s request to appoint a special master to review records seized in the FBI search, a move that is likely to delay the Justice Department’s criminal investigation.