Former U.S. President Donald Trump said FBI agents raided his Mar-a-Lago estate on Monday and broke into his safe in what his son acknowledged was part of an investigation into Trump's removal of official presidential records from the White House to his Florida resort.

The unprecedented search of a former president's home would mark a significant escalation into the records investigation, which is one of several probes Trump is facing from his time in office and in private business.

The U.S. Justice Department declined to comment on the search, which Trump in a statement said involved a "large group of FBI agents." The FBI's headquarters in Washington and its field office in Miami both declined comment.

Eric Trump, one of the former president's adult children, told Fox News the search concerned boxes of documents that Trump brought with him from the White House, and that his father has been cooperating with the National Archives on the matter for months.

A source familiar with the matter also confirmed to Reuters the raid appeared to be tied to Trump's removal of classified records from the White House. 

Trump said the estate "is currently under siege, raided, and occupied." He did not say why the raid took place. 

"After working and cooperating with the relevant government agencies, this unannounced raid on my home was not necessary or appropriate," Trump said, adding: "They even broke into my safe!"

Trump was not present at the time as he was in New York on Monday, Fox News Digital reported, publishing a photo of Trump that a Fox reporter said showed him leaving Trump Tower.

Trump, who has made his club in Palm Beach his home since leaving the White House in January 2021, has generally spent summers at his golf club in Bedminster, New Jersey, because Mar-a-Lago typically closes for the summer.

A federal law called the U.S. Presidential Records Act requires the preservation of memos, letters, notes, emails, faxes and other written communications related to a president's official duties.

Any search of a private residence would have to be approved by a judge, after the investigating law-enforcement agency demonstrated probable cause that a search was justified.

It almost certainly would also be approved by FBI Director Christopher Wray, a Trump appointee, and his boss, Attorney General Merrick Garland, who was appointed by Trump's successor and political rival, President Joe Biden.

Democratic supporters of Biden have criticized Garland for being overly cautious in investigating Trump over his attempts to overturn his 2020 election loss to Biden.

But Trump supporters in turn have accused the Democrats of weaponizing the federal bureaucracy to target Trump, even as Biden has taken steps to distance himself from the Justice Department.

"Make no mistake, the attorney general had to authorize this," said Phillip Halpern, a former federal prosecutor who specialized in public corruption cases, adding that Wray and a host of prosecutors would also be involved.

"This is as big a deal as you can have, and ... every single person in the chain would have had to sign off on this," Halpern said.