The FBI was looking for classified documents relating to nuclear weapons when it raided former US president Donald Trump's Florida home, according to US press reports.
The Washington Post reported today that the dramatic search reflected "deep concern among government officials about the types of information they thought could be located at Trump's Mar-a-Lago club".
There was no confirmation that such documents were found or located in the FBI raid this week which is believed to have seized 10 to 15 boxes of material, in addition to the 15 boxes previously returned to the government by Trump in January.
The law enforcement sources, who spoke on the condition of anonymity to discuss an ongoing investigation, did not say whether the classified documents in question involved information about nuclear weapons belonging to the United States or some other nation.
Meanwhile, US Attorney General Merrick Garland has revealed that he personally authorised the decision to seek court permission for a search warrant.
"The Justice Department does not take such a decision lightly. Where possible, it is standard practice to seek less intrusive means as an alternative to a search and to narrowly scope any search that is undertaken," he said.
He now wants elements of the search warrant unsealed so the public can understand the reasons for the raid. Garland noted that agents had tried to conduct the search without drawing significant public attention, but Trump himself had made it public.
"The public's clear and powerful interest in understanding what occurred under these circumstances weighs heavily in favour of unsealing," the Justice Department's motion to unseal the warrant says.
"That said, the former president should have an opportunity to respond to this motion and lodge objections, including with regard to any 'legitimate privacy interests' or the potential for other 'injury' if these materials are made public."
The bombshell claim that the FBI was looking for documents relating to nuclear weapons comes as former Australian prime minister John Howard described Trump's behaviour in the wake of his 2020 election defeat, refusing to accept the outcome, as "appalling" and "atrocious".
Writing in a new book A Sense of Balance, Howard said Trump was unfit for office.
"Trump's atrocious behaviour after losing the 2020 election … has surely made him unfit to return to the White House," Howard writes.
"It was dumbfounding to me, and I am sure to many others, that the party should have chosen him as its candidate in 2016."
Two dozen FBI agents and technicians arrived at Trump's Florida home to execute a search warrant on Monday in an investigation believed to involve provisions of the 1978 Presidential Records Act.
But one Justice Department official told the Washington Post that the type of top-secret information described by the people familiar with the probe could trigger grave harm to US security.
"If that is true, it would suggest that material residing unlawfully at Mar-a-Lago may have been classified at the highest classification level," said David Laufman, the former chief of the Justice Department's counterintelligence section, which investigates leaks of classified information.
"If the FBI and the Department of Justice believed there were top secret materials still at Mar-a-Lago, that would lend itself to greater 'hair-on-fire' motivation to recover that material as quickly as possible."
Trump said in a statement, "This unannounced raid on my home was not necessary or appropriate.
"Such an assault could only take place in broken, Third World countries. Sadly, America has now become one of those countries, corrupt at a level not seen before."
Earlier this week, Newsweek reported that the FBI search of Trump's residence was sparked by an "FBI confidential human source" in the Trump camp who knew which documents to look for and where they were located.
According to the Newsweek report, and a separate one in the Wall Street Journal, the search was "deliberately timed to occur when the former president was away".
Trump voluntarily handed over more than a dozen boxes of material earlier this year.
Those records reportedly included letters from North Korean dictator Kim Jong Un — correspondence Trump had referred to as "love letters" — and other classified material, prompting the National Archives to consult with the Justice Department.
"I was really tough and so was he, and we went back and forth," Trump told a rally in 2018 of his relationship with the North Korean dictator.
"And then we fell in love, okay? No, really, he wrote me beautiful letters, and they're great letters. We fell in love.
"The ones I did best with were the tyrants. For whatever reason, I got along great with them."
Supporters, including former Trump administration official Kash Patel, insist Trump declassified the material he took to Mar-a-Lago.
"Trump declassified whole sets of materials in anticipation of leaving the government that he thought the American public should have the right to read themselves," he said.
"The White House counsel failed to generate the paperwork to change the classification markings, but that doesn't mean the information wasn't declassified."