A man who threatened to assassinate Joe Biden has been shot dead during an FBI raid in Utah, hours before the US president was due to visit the state.

It's understood Craig Robertson posted multiple threats to Facebook against several high-profile figures, including Biden, Vice-President Kamala Harris, and Alvin Bragg, the Manhattan district attorney leading the investigation into an alleged hush money payment by Donald Trump to an adult film star.

The raid took place on Tuesday morning at 6:15am local time in a town 65km south of Salt Lake City.

Robertson had reportedly posted a series of threatening messages to his Facebook, many of which heavily featured guns and other combat equipment.

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It's understood Robertson came to the attention of the FBI back in March when he took to Truth Social, the platform founded by Donald Trump, to threaten district attorney Alvin Bragg.

The platform flagged Robertson's activity and the FBI visited him at his home where he reportedly told them the post was a "dream" and said: "We're done here! Don't return without a warrant!"

United States President Joe Biden walks on the South Lawn of the White House (file photo)
United States President Joe Biden walks on the South Lawn of the White House (file photo)

However, Robertson's catalogue of threats reportedly stretches further back than just this year. It's reported that he wrote on Facebook last November: "The time is right for a presidential assassination or two. First Joe then Kamala!!!"

Further posts allegedly posted by Robertson feature him dressed in camouflage threatening public officials such as attorney general Merrick Garland and New York attorney general Letitia James.

A previous post reportedly said: "I hear Biden is coming to Utah. Digging out my old ghillie suit and cleaning the dust off the M24 sniper rifle."

Another alleged to have been posted to Facebook said: "Perhaps Utah will become famous this week as the place a sniper took out Biden the Marxist."

A neighbour who witnessed the raid told local news: "I couldn’t see much from where I was, I could just hear." He then said he heard loud booms which he assumed were flashbang grenades.

"They started talking over their microphone saying, 'Craig Robertson, please come out with your hands up.' They did that a few times," he added.

Court documents show that Robertson had been charged with three felony counts, one of which was making threats to the life of the president.

A spokesperson for the Utah office of the FBI said: "The FBI takes all shooting incidents involving our agents or taskforce members seriously. In accordance with FBI policy, the shooting incident is under review by the FBI’s Inspection Division. As this is an ongoing matter, we have no further details to provide."

Biden arrived in Utah on Wednesday night as part of his tour of the western United States to canvas and take part in re-election fundraisers.