Washington (AFP)

Donald Trump declared on Monday he was annulling pardons issued by Joe Biden to shield Trump critics from retribution, claiming that they were invalid because his Democratic predecessor had supposedly used an autopen for his signature.

It was unclear what, if any, authority Trump has to void presidential pardons issued by his predecessor.

It is extremely rare for pardons to be revoked in US history, and doing so in this case could see Trump again testing the limits of executive power.

Trump claimed that Biden's signature on the documents had been carried out with an autopen, a commonly used device, and therefore was not valid.

The pardons "are hereby declared void, vacant, and of no further force or effect, because of the fact they were done by Autopen," Trump posted on his social media account Truth Social.

However, he provided no evidence either for the use of an autopen or his contention that it would invalidate the signature.

US presidents have long used autopens, including to sign bills into law.

Biden issued pardons to former senior Republican lawmaker Liz Cheney and other members of the congressional committee that had investigated the January 6, 2021 attack on the Capitol.

Asked by reporters early Monday whether everything Biden signed with an autopen should be voided, Trump said "I think so. It's not my decision, that'll be up to a court."

But he said on Truth Social that the committee members "should fully understand that they are subject to investigation at the highest level."

Biden also issued preemptive pardons to former Covid pandemic advisor Anthony Fauci, retired general Mark Milley, and his son Hunter.