A document describing a foreign country's military defenses was found in the FBI's search of former President Donald Trump's home last month, The Washington Post reported on Tuesday.
The report, which cited unnamed sources familiar with the case, did not name the country that was discussed in the document.
The descriptions in the document included the country's nuclear capabilities, according to the report.
No details were given as to where in the residence the documents were found or what kind of security was present there.
Documents reportedly highly classified
The Post reported that some of the documents seized on August 8 in the FBI raid of Mar-a-Lago detailed top-secret US operations that were not known by senior national security officials.
The newspaper's sources said that only the president, some cabinet members or officials near the level of seniority of cabinet members could authorize other officials to know details of the programs.
According to the Post, such documents require special clearances on a need-to-know basis.
According to a court filing, "even the FBI counterintelligence personnel and DOJ attorneys conducting the review required additional clearances before they were permitted to review certain documents" found in the raid.
The FBI declined to comment when asked about the report, Reuters news agency said.