Washington Post report did not identify foreign government discussed in document that FBI seized from Trump's Florida house, nor did it indicate whether the country was friendly or hostile to US.
A document describing a foreign government's military defences, including its nuclear capabilities, has been found in the FBI's search last month of ex-president Donald Trump's Florida home, the Washington Post reported.
Tuesday's report, which cited people familiar with the matter, did not identify the foreign government discussed in the document, nor did it indicate whether the foreign government was friendly or hostile to the United States.
Trump representatives and the Justice Department did not immediately respond to requests for comment from the Reuters news agency.
The FBI recovered more than 11,000 government documents and photographs during its August 8 search at 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.
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.