FBI agents were looking for secret documents about nuclear weapons among other classified material when they searched Donald Trump’s home on Monday, it has been reported.

The Washington Post cited people familiar with the investigation as saying nuclear weapons documents were thought to be in the trove the FBI was hunting in Trump’s Mar-a-Lago resort. They did not specify what kind of documents or whether they referred to the US arsenal or another country’s.

The report came hours after the attorney general, Merrick Garland, said he had personally authorised the government request for a search warrant and revealed that the justice department had asked a Florida court for the warrant to be unsealed, noting that Trump himself had made the search public.

The justice department motion referred to “the public’s clear and powerful interest in understanding what occurred in its contents”.

Trump later released a statement saying he would not oppose but rather was “encouraging the immediate release of those documents” related to what he called the “unAmerican, unwarranted, and unnecessary raid and break-in … Release the documents now!”

Garland’s announcement followed a furious backlash to the search from Trump supporters who portrayed it as politically motivated. On Thursday a man who tried to breach the FBI’s Cincinnati office was shot and killed by police after he fled the scene.

The court told the government to present its motion to Trump’s lawyers and to report back by 3pm on Friday on whether Trump objected to the warrant being unsealed.

The suspected presence of nuclear weapons documents at Mar-a-Lago could explain why Garland took such a politically charged step as ordering FBI agents into a former president’s house, as retrieving them would be seen as a national security priority.

Trump was particularly fixated on the US nuclear arsenal while he was in the White House, and boasted about being privy to highly secret information.

In the summer of 2017 he told US military leaders he wanted an arsenal comparable to its cold war peak, which would have involved a ten-fold increase, a demand that reportedly led the then secretary of state, Rex Tillerson, describe him as a “fucking moron”. Trump publicly threatened to obliterate both North Korea and Afghanistan.

In his book on the Trump presidency, Rage, Bob Woodward quoted the former president as telling him: “We have stuff that you haven’t even seen or heard about. We have stuff that Putin and Xi have never heard about before. There’s nobody – what we have is incredible.”

Woodward said he was later told the US did indeed have an unspecified new weapons system, and officials were “surprised” that Trump had disclosed the fact.

Cheryl Rofer, a chemist who worked on nuclear weapons at the Los Alamos national laboratory said there were varying classification levels applying to different kinds of documentation.

“Information about the design of nuclear weapons is called Restricted Data and is ‘born classified’. That means it is assumed to be classified unless declassified,” Rofer, who writes a blog titled Nuclear Diner, wrote on Twitter. But she added: “There’s no reason for a president to have nuclear weapons design information that I can see.”

Among the nuclear documents that Trump would routinely have had access to would be the classified version of the Nuclear Posture Review, about US capabilities and policies. A military aide is always close to the president carrying the “nuclear football”, a briefcase containing nuclear strike options, but it would be unusual for those documents to be taken out of the football.

Another possibility Rofer pointed to is that Trump could have retained his nuclear “biscuit”, a piece of plastic like a credit card with the identification codes necessary for nuclear launch. Those codes would have been changed however the moment Biden took office at noon on 20 January 2021.