US Attorney General Merrick Garland has said that he had "personally approved" the search of Donald Trump's Florida home, and condemned "unfounded attacks" on the FBI following the unprecedented action against an ex-US president.
Garland did not explain the reason for the search on Thursday but stressed there was "probable cause" and said he has asked a court to make the case's documents public.
"I personally approved the decision to seek a search warrant in this matter," he told reporters. "The department does not take such a decision lightly."
Leading Republicans have rallied around Trump, who was not present when the raid took place.
Garland said the Justice Department had asked a court to publish a sealed search warrant "in light of the former president's public confirmation of the search, the surrounding circumstances and the substantial public interest in this matter."
It was not clear whether Trump's legal team would object to the release of the warrant, which could shed light on the nature of the investigation.
In a statement on his ‘Truth Social’ network, Trump said: "My attorneys and representatives were cooperating fully, and very good relationships had been established. The government could have had whatever they wanted if we had it."
The unprecedented search marked a significant escalation in one of the many federal and state investigations Trump is facing during his time in office and in private business.
FBI agents visited Trump's property earlier this year to investigate boxes in a locked storage room, according to a person familiar with the visit. The agents and a Trump lawyer, Evan Corcoran, spent a day reviewing materials, the source said.
A second source who had been briefed on the matter told Reuters news agency that the Justice Department also has surveillance footage from Mar-a-Lago in its possession.
Trump supporters, and some of his fellow Republicans in Washington, have accused Democrats of "weaponising" the federal bureaucracy to target Trump.
The FBI said an armed person had tried to breach its office in Cincinnati early on Thursday in what it called a "critical incident." Local law enforcement said officers exchanged fire with a male suspect wearing body armour.
Garland condemned the attacks on employees of the FBI and Justice Department.
"I will not stand by silently when their integrity is unfairly attacked," he said.