Washington DC - A panel of federal appeals court judges appeared deeply skeptical of Donald Trump's claim that as a former president, he should be immune from prosecution on charges he conspired to overturn the 2020 election.

The 77-year-old attended the US Court of Appeals hearing on Tuesday, held under tight security in a Washington courthouse just blocks away from the US Capitol, which was stormed by his supporters on January 6, 2021.

Trump, the front-runner for the 2024 Republican presidential nomination, listened quietly to the arguments in front of a three-judge panel as he is scheduled to go on trial on March 4 on charges of conspiring to overturn the 2020 election.

The former president's attorney John Sauer told the judges that a president can only be prosecuted for actions taken while in the White House if they have first been impeached and convicted by Congress.

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"To authorize the prosecution of a president for his official acts would open a Pandora's Box from which this nation may never recover," Sauer argued.

"The notion that criminal immunity for a president doesn't exist is a shocking holding," he added. "It would authorize, for example, the indictment of President Biden in the Western District of Texas after he leaves office for mismanaging the border."

District Judge Tanya Chutkan, who is to preside over Trump's trial, rejected his immunity claim last month and the judges who heard his appeal on Tuesday also appeared unconvinced.

"I think it's paradoxical to say that his constitutional duty 'to take care that the laws be faithfully executed' allows him to violate criminal laws," said Judge Karen Henderson, an appointee of former Republican President George H. W. Bush.

Judge Florence Pan, who was appointed by President Joe Biden, asked Sauer whether a president could be criminally prosecuted for ordering the assassination of a political rival by Navy SEAL special forces.

Sauer insisted that even in this case, a president could only be tried if first impeached and convicted by Congress.

James Pearce, a Justice Department attorney, called that an "extraordinarily frightening" prospect and said it would allow a president to resign before being impeached and escape punishment.

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"Never before has there been allegations that a sitting president has with private individuals and using the levers of power sought to fundamentally subvert the democratic republic and the electoral system," Pearce said.

"The president has a unique constitutional role, but he is not above the law," he added.

Trump, who was not required to attend the hearing, told reporters afterward that he believed it was "very unfair" he was being pursued by the Justice Department under Biden, his likely 2024 election opponent.

"They feel this is the way they're going to try and win," Trump said. "And that's not the way it goes. It will be bedlam in the country."