Former President Donald Trump has launched a sustained attack on Mr Biden's handling of the retreat of US forces from Afghanistan, which he called "the greatest foreign policy humiliation" in US history.

Mr Trump, a Republican who has dangled the possibility of running again for president in 2024, has repeatedly blamed Mr Biden, a Democrat, for Afghanistan's fall to the Taliban, even though the US withdrawal that triggered the collapse was negotiated by his own administration.

"Biden’s botched exit from Afghanistan is the most astonishing display of gross incompetence by a nation’s leader, perhaps at any time," Mr Trump said at a boisterous rally packed with his supporters near Cullman, Alabama.