Joe Biden has pre-emptively pardoned Covid response chief Anthony Fauci and the members of the 6 January riot investigation to prevent what he called "unjustified... politically motivated prosecutions".

The outgoing US president said: "Our nation owes these public servants a debt of gratitude for their tireless commitment."

Trump, who will be inaugurated on Monday, regularly clashed with Dr Fauci during the pandemic and has suggested he would take action against those who tried to hold him accountable for the 6 January Capitol riot.

Biden also issued a pre-emptive pardon to Mark Milley, a former chairman of the Join Chiefs of Staff, who last year described Trump as "fascist to the core".

Biden's statement said that the pardons should "not be mistaken as an acknowledgment" that any of those covered "engaged in any wrongdoing".

Democrats had warned the outgoing president against such action. Adam Schiff, a Senator for California, said Biden could set a "precedent" for "each president hereafter on their way out the door giving out a broad category of pardons".

Dr Fauci told US media that he "truly appreciated" Biden for taking action, adding that the possibility of prosecution has created "immeasurable and intolerable distress" on his family.

"Let me be perfectly clear, I have committed no crime and there are no possible grounds for any allegation or threat of criminal investigation or prosecution of me," he added.

General Milley, 66, thanked Biden in a statement and stated that he did not wish spend the rest of his life "fighting those who unjustly might seek retribution for perceived slights".

"I do not want to put my family, my friends, and those with whom I served through the resulting distraction, expense, and anxiety," he said.

Biden's pardons cover all members of the House Select Committee investigating the 6 January riot, as well as their staff members and the officers who testified.

Former US Capitol Police officer Harry Dunn said he was "eternally grateful" to Biden, "not just for this pre-emptive pardon, but for his leadership and service to this nation".

"Unfortunately, the political climate we are in now has made the need for [a pardon] somewhat of a reality," he said.

"I, like all other public servants, was just doing my job and upholding my oath."

Trump in December backed a call for the FBI to investigate fellow Republican Liz Cheney over her role in leading Congress's probe.

The incoming president is set to pardon some of those convicted of crimes related to the riot. "You're going to see something tomorrow," Trump said on Sunday, in reference to the 6 January rioters. "I think you'll be very, very happy."

On the campaign trail, Trump railed against "enemies from within", and has endorsed several figures who have vowed retribution against his foes to join his cabinet.

However, his choice for attorney general, Pam Bondi, said during her confirmation hearing last week that there would never be an enemies list and that she would not use the Justice Department to target anyone based on their politics.