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US President will "bear grudges" against UK leaders for their opposition to his decision to withdraw , including comments about his mental state, his allies have told The Telegraph.

UK cabinet staff had been reported by British media as saying that Biden was "doolally" and "looked gaga" in the aftermath of Afghan capital Kabul's fall to the .

"It's always been his way that if somebody says something really bad to him, or about him, he doesn't speak to them again. He does bear grudges. Boris Johnson should know that," one American ally of the president told the British daily.

Biden has been widely criticised for his stubborn commitment to the withdrawal of US troops from Afghanistan by 31 August.

UK politicians, including Prime Minister Boris Johnson, have against that date.

The source said the resistance from the UK, an ally with which the US is commonly said to have a "special relationship", could do great damage to ties between the two countries.

"Johnson needs to take dramatic action to secure the relationship," he said.

The 77-year-old US president's mental state, particularly his memory, has been scrutinised by the media and his political opponents before.

Biden multiple times in a speech he made in June.

The president has put those down to being gaffe-prone, describing himself as a "gaffe machine" in 2018.

Biden's decision to pull US troops from Afghanistan has been widely criticised by NATO allies who do not believe they were properly consulted on the matter.

The withdrawal forced NATO countries to plan a messy and hasty exit from Afghanistan of their own citizens, troops, and Afghan allies.

Security in the country has also collapsed after the Taliban's takeover of the capital, with the Islamic State group targeting Afghans and US troops at Kabul Airport during the evacuations.

Johnson has also been criticised in the UK for the withdrawal.