US Attorney General Merrick Garland said he "personally" approved the FBI search on Donald Trump's Florida home, and would seek legal approval to reveal more details of why a search warrant had been issued.

US Attorney General Merrick Garland said Thursday that the Justice Department had asked a court to unseal the search warrant for former US President Donald Trump's Florida home.

He cited "substantial public interest in this matter" in unsealing the search warrant and itemized receipt of what was seized. It was the first time Garland publicly spoke about the raid.

FBI agents searched Trump's Mar-a-Lago property on Monday, reportedly searching for classified documents that should have been turned in after his presidency.

The unannounced operation on his Florida home was a politically explosive escalation of a federal investigation into whether Trump illegally removed records from the White House.

Garland did not provide further details on the search, or the details of the warrant, but underscored that his department would not undertake such a search lightly.

Garland said he personally approved the FBI's search of Trump's property.

It was unclear if and when the court would unseal the documents, but the motion to do so appeared to confirm the raid was searching for classified documents.

"The occurrence of the search and indications of the subject matter involved are already public," the Justice Department wrote in a court filing, citing a New York Times article on the raid.

Trump and his lawyers have copies of the documents, but have not shared them with the public.