Joe Biden has issued pre-emptive pardons for former chairman of the US Joint Chiefs of Staff Mark Milley and former White House chief medical adviser Anthony Fauci in his final hours as US President.

Biden used the extraordinary powers of his office to guard against potential “revenge” by the incoming administration of Donald Trump.

The pardon also covers all politicians who served on the congressional select committee that investigated the January 6, 2021, storming of the US Capitol by Trump supporters, and police officers who testified before it.

Trump, who returned to the presidency later on Monday (local time), has called for the punishment of his perceived enemies since winning the US presidential election in November.

Biden praised public servants as the “lifeblood of our democracy.”

Without mentioning Trump, he expressed alarm in a statement that some were subjected to threats and intimidation for doing their job.

“These public servants have served our nation with honour and distinction and do not deserve to be the targets of unjustified and politically motivated prosecutions,” Biden said.

“Rather than accept accountability, those who perpetrated the January 6th attack have taken every opportunity to undermine and intimidate those who participated in the select committee in an attempt to rewrite history, erase the stain of January 6th for partisan gain and seek revenge, including by threatening criminal prosecutions.”

In December, Trump backed a call for the FBI to investigate fellow Republican Liz Cheney over her role in leading the US Congress probe of the January 6 riots at the Capitol.

Fauci often clashed with Trump during the Covid-19 pandemic. Trump’s supporters and libertarians have continued to criticise the former senior health official, who they blame for mask mandates and other policies they believe infringed on people’s rights.

Milley was quoted in the book War by Bob Woodward, published last month, calling Trump “fascist to the core”.

Just before he handed over the office to Trump, Biden also pardoned five members of his family, saying he wanted to protect them from politically-motivated investigations.

He pardoned his siblings – James Biden, Frank Biden and Valerie Biden Owens – as well as their spouses, John Owens and Sara Biden.

“My family has been subjected to unrelenting attacks and threats, motivated solely by a desire to hurt me – the worst kind of partisan politics,” Biden said.

“Unfortunately, I have no reason to believe these attacks will end.”

It is customary for a US president to grant clemency at the end of his term but those acts of mercy are usually offered to everyday citizens who have been convicted of crimes.

Biden has used the power in the broadest and most untested way possible: To pardon those who have not even been investigated yet.

With the acceptance comes a tacit admission of guilt or wrongdoing, even though those who have been pardoned have not been formally accused of any crimes.

The decision lays the groundwork for an even more expansive use of pardons by Trump and future presidents.

It is unclear whether those pardoned by Biden would need to apply for the clemency or even accept the offer at all.

“These are exceptional circumstances, and I cannot in good conscience do nothing,” Biden said.

“Even when individuals have done nothing wrong – and, in fact, have done the right thing – and will ultimately be exonerated, the mere fact of being investigated or prosecuted can irreparably damage reputations and finances.”

-with AAP