The FBI move marked a stunning escalation of legal probes into the 45th president and comes as he is weighing another White House run.
Several former advisors to the 76-year-old Trump urged him to immediately confirm that he would be a presidential candidate in 2024.
“Nothing like this has ever happened to a President of the United States before,” Trump said of the FBI operation at his Mar-a-Lago resort in West Palm Beach.
He denounced the FBI raid as a “weaponization of the Justice System” by “Radical Left Democrats who desperately don’t want me to run for President in 2024.”
At the White House, Press Secretary Karine Jean-Pierre said President Joe Biden did not have any advance notice about the raid and respected the independence of the Justice Department.
Asked about the potential for civil unrest in reaction to Trump’s legal problems, Jean-Pierre said “there’s no place for political violence in this country.”
The FBI, which is led by Christopher Wray, a Trump appointee, declined to provide a reason for the raid.
But US media outlets said agents were conducting a court-authorised search related to the potential mishandling of classified documents that had been sent to Mar-a-Lago after Trump left the White House in January 2021.
Trump has also faced intense legal scrutiny for his efforts to overturn the results of the 2020 election and over the Jan 6 attack on the US Capitol by his supporters.
Since leaving office, Trump has remained the country’s most divisive figure, continuing to sow falsehoods that he actually won the 2020 vote.
A day after the raid on Mar-A-Lago, US Representative Scott Perry - a Trump ally - said that FBI agents had confiscated his cell phone, but did not specify why it was taken.
“This morning, while traveling with my family, three FBI agents visited me and seized my cell phone,” Perry told FOX News, condemning “these kinds of banana republic tactics.”
Allies rally round
Leading Republicans rallied around the former president, who was not present at Mar-a-Lago when the raid took place.
Trump’s former vice president Mike Pence, a potential 2024 rival, expressed “deep concern” and said the raid smacked of “partisanship” by the Justice Department.
Kevin McCarthy, who is seeking to become speaker of the House of Representatives if Republicans win November’s midterm elections, accused the Justice Department of “weaponized politicization.”
Republican Senator Lindsey Graham, a Trump ally, said “launching an investigation of a former president this close to an election is beyond problematic.”
Representative Elise Stefanik, the third-ranking House Republican, called it a “dark day in American history.”
“If the FBI can raid a US President, imagine what they can do to you,” Stefanik tweeted, to which Democratic Representative Ted Lieu replied: “Why can’t the FBI investigate a US President? We’re not Russia, where the law doesn’t apply to the head of state and his cronies.”
Nancy Pelosi, the Democratic speaker of the House, told NBC that “no person is above the law.”
In his statement, Trump did not give any indication about why the FBI raided his home but said: “They even broke into my safe!”
Andrew McCabe, a former FBI deputy director, told CNN that agents may have been looking for “something specific” related to the probe into the handling of classified information.
The National Archives said in February that it had recovered 15 boxes of documents from Mar-a-Lago and asked the Justice Department to look into Trump’s handling of classified material.
The recovery of the boxes raised questions about Trump’s adherence to presidential records laws enacted after the 1970s Watergate scandal that require Oval Office occupants to preserve records.
Trump’s former communications director Alyssa Farah Griffin told CNN the raid could fire up his supporters, a small number of whom rallied outside Mar-a-Lago yesterday.
“If it’s seen as some sort of massive overreach and not something incredibly serious, this is a very good day for Donald Trump,” Farah Griffin said.
For weeks, Washington has been riveted by hearings in Congress about the Jan 6 storming of the Capitol and Trump’s attempts to overturn the 2020 election.
Attorney General Merrick Garland has been repeatedly pushed over whether the Justice Department is building a case against Trump over the Capitol riot.
Trump is also being investigated for his efforts to alter the 2020 voting results in the state of Georgia, while his business practices are being probed in New York in separate cases.