Donald Trump orders probe into alleged cover-up of ex-US president Joe Biden's health decline

President Trump has initiated an investigation into alleged cover-up claims regarding Joe Biden's cognitive health during his presidency.

US President Donald Trump on Wednesday (local time) initiated an investigation into allegations by Republicans that former President Joe Biden’s cognitive decline was deliberately concealed during his time in office.

US President Donald Trump with his his predecessor Joe Biden.(REUTERS file)

"This conspiracy marks one of the most dangerous and concerning scandals in American history," a presidential memorandum reads.

Donald Trump's move comes after running a campaign to discredit his predecessor, which has been joined by Republican Party politicians and their cheerleaders in conservative media.

They cite Joe Biden's infrequent public appearances while in office and his apparent unwillingness to sit for interviews as evidence of a man incapable of doing the demanding job of commander-in-chief of the United States.

They allege that Biden's aides covered up his physical and mental deterioration, made key decisions on his behalf, and used a signature-replicating device to govern the country in his name.

"The Counsel to the President, in consultation with the Attorney General and the head of any other relevant executive department or agency... shall investigate... whether certain individuals conspired to deceive the public about Biden's mental state and unconstitutionally exercise the authorities and responsibilities of the President," news agency AFP reported, citing Wednesday's document.