FBI agents searched the Bethesda, Maryland, home of John Bolton, former national security adviser to US President Donald Trump, on Friday as part of an investigation.

Trump said he had limited knowledge of the search of his former associate's home, but did not hesitate to call him a bastard.

I'm not a fan of John Bolton. He's really some kind of bastard, he told reporters, adding that he would likely be briefed by the Justice Department later in the day.

The two men's feud has flared up again recently. After Trump's meeting with Vladimir Putin in Alaska, Bolton told CNN that the Russian president clearly won the meeting, while Trump didn't lose, but he seemed very tired and there was no substantial progress on ending the war in Ukraine.

The operation began at 7 am and, according to the announcement by the Federal Service, it was an activity following a court order.

FBI Director Cass Patel, who ordered the investigation, wrote in a post on Platform X: No one is above the law… FBI agents on a mission, without naming Bolton.

Bolton himself told CNN that he knew nothing about the operation and that he was investigating it further.

Bolton, who served as US ambassador to the United Nations and as national security adviser in the White House during Trump's first term, has become a fierce critic of the Republican president.

In his book The Room Where It Happened: A White House Memoir, he had characterized Trump as unfit to serve, provoking the wrath of the then White House, which in 2020 attempted to block its publication and opened a criminal investigation for leaking classified information. Both cases were closed in 2021 under the Biden administration.

Bolton has also personally attacked Patel, telling NBC last year that the Senate should have rejected his nomination to head the FBI by a vote of 100-0. The Senate nevertheless approved the nomination.

The search of Bolton's home comes at a time when Trump, in his second term, has pledged to use the tools of power to turn against those he considers his political opponents, as part of the revenge that he had already announced during his election campaign.