The FBI agents were looking for documents relating to nuclear weapons, among others, in the unprecedented search they conducted of the premises of former US President Donald Trump earlier this week in Florida, according to a stunning news report.

Neither the US Justice Department, which oversees the FBI, nor the investigating agency denied or confirmed the Thursday evening report by The Washington Post.

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The newspaper sourced the report to multiple officials "all unidentified" involved in the investigation of the case that caused the search but gave no further details of the kind of nuclear weapons' documents sought by the agents.

Government officials are worried that these documents could fall in the wrong hands at Trump's Florida home that is also a club frequented by members.

Trump has held on to an undisclosed volume of documents from his presidency that he is required to have turned in for archiving by the government. The National Archive, which is the repository of these documents, has been following up with him and his aides for months.

The FBI agents searched Trump's home in an unprecedented first for a US President on Monday, according to a statement from Trump, who called it a "raid" in a political ploy to both discredit it and rile up his base with a familiar story of victimhood he had used against the Russia investigation and his double impeachment.

As allies and followers predictably poured scorn and outrage on the "raid", Trump and his lawyers did not tell them and the country the details that were available to them by way of the search warrant issued by a federal judge, which would have contained the grounds for it, or the itemized list of articles taken by the FBI "at least 15 boxes" that were duly provided to them.

Trump was once again the hounded hero for his followers "including many lawmakers" who had no idea why his premises were searched.

US Attorney General Merrick Garland, who heads the Justice Department that has oversight of the FBI, called the former President's bluff.

Garland in rare public remarks said "the Justice Department doesn't comment on ongoing investigation" said the government has filed a motion in a Florida federal court asking for unsealing the search warrant and all related documents. He offered no details of the investigation.

The public's clear and powerful interest in understanding what occurred under these circumstances weighs heavily in favour of unsealing, the motion said.

"That said, the former President should have an opportunity to respond to this motion and lodge objections, including with regards to any "legitimate privacy interests" or the potential for other "injury" if these materials are made public."

There was no comment from Trump and his lawyers to this development for hours after Garland's statement.