Trump UK visit: President launches extraordinary attack on 'stone cold loser' Sadiq Khan moments before arrival

'Kahn (sic) reminds me very much of our very dumb and incompetent Mayor of NYC,' US leader tweets

Donald Trump has launched an extraordinary attack on London mayor Sadiq Khan just moments before touching down in the UK for his state visit.

".@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly 'nasty' to the visiting President of the United States, by far the most important ally of the United Kingdom," Mr Trump tweeted on Monday morning while aboard Air Force One.

"He is a stone cold loser who should focus on crime in London, not me.

"Kahn (sic) reminds me very much of our very dumb and incompetent Mayor of NYC, de Blasio, who has also done a terrible job - only half his height. In any event, I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit. Landing now!"

Minutes later, Mr Trump landed at Stansted Airport, where he was due to head from there to Buckingham Palace for a reception with the Queen, Prince of Wales and the Duchess of Cornwall.

Mr Trump had also insulted Mr Khan before departing for Britain, telling reporters outside the White House on Sunday evening, "I don't think much of him", before making fun of his stature.

"I think that he's a - he's the twin of (New York City mayor Bill) de Blasio, except shorter," Mr Trump said.

It came after Mr Khan described the US president over the weekend as "just one of the most egregious examples of a growing global threat" and compared the language he had used to that of the "fascists of the 20th century".

Mr Trump's description of Mr Khan as "nasty" appeared to be a reference to a row over the president's description of the Duchess of Sussex in comments made to The Sun.

He denied calling her "nasty" and said he would not apologise to the Royal Family.