FBI agents reportedly searched for documents relating to nuclear weapons at former President Donald Trump's home in Florida this week.
It was not clear if such documents were recovered.
It marks the first time a former US president's home has ever been searched by law enforcement.
FBI activity is reportedly linked to an investigation into whether Trump removed classified records from the White House and took them to Mar-a-Lago.
According to the Washington Post on Thursday U.S. federal agents were looking for documents relating to nuclear weapons when they raided the home.
The search was approved at the highest levels of the Department of Justice (DoJ), an unnamed US official told CBS News.
Writing on the Truth Social website Trump left a string of messages, including one that said in capital letters 'witch hunt.'
Republicans have branded the search politically motivated.
Former Vice-President, Mike Pence, who has subtly distanced himself amid speculation they may both launch 2024 White House runs, called on the attorney general to give "a full accounting" of why the search warrant was carried out.
White House spokeswoman Karine Jean-Pierre said President Joe Biden was given no advance notice by the FBI of the raid, and claimed he "learned about this from public reports".
She told reporters: "The president was not briefed and was not aware of it. No-one at the White House was given a heads-up," she said.
After reports of the raid spread, a mob of die-hard Donald Trump supporters stormed the streets outside his Mar-a-Lago home after the FBI searched his estate as part of a criminal investigation.
Demonstrators thronged around the Florida manor lifting signs and flags declaring their support for the ex-president.
Some hoisted banners calling him to run in 2024, while others lifted placards slamming Joe Biden and rejecting his 2020 win.
Another protester lifted a sign from his previous campaign but with former Vice President Mike Pence's name crossed out after the VP was branded a "traitor" by some sections of the American far right.
One of the men gathered identified himself as a member of the neo-fascist Proud Boys group.
Supporters say the raid is a brazen attempt to derail Trump from an upcoming presidential run, which he has yet to confirm.
His followers on social media have predicted the uproar could trigger a second civil war - with some geared up to take on their political nemeses.
Disclosing the search in a lengthy statement, the former US president said agents opened up a safe at his home and described their work as an "unannounced raid" that he likened to "prosecutorial misconduct".
The news has angered Mr Trump's supporters in the US, some of whom were involved in the infamous Capitol Hill riots in January last year.
