Sadiq Khan's office has hit back at "far-right" Donald Trump after the US president launched an extraordinary attack on the London mayor moments ahead of landing in the UK.
Minutes before touching down outside the capital aboard Air Force One, Mr Trump branded Mr Khan a "stone cold loser" who had done a "terrible job" as mayor.
He also compared the former Labour MP to New York City's mayor Bill de Blasio, who Mr Trump dislikes, and insulted his stature.
"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," Mr Trump tweeted on Monday morning.
In response, a spokesperson for Mr Khan said: "This is much more serious than childish insults which should be beneath the President of the United States.
"Sadiq is representing the progressive values of London and our country warning that Donald Trump is the most egregious example of a growing far-right threat around the globe, which is putting at risk the basic values that have defined our liberal democracies for more than 70 years."
The war of words was sparked when 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".
After landing at Stansted Airport, Mr Trump was due to head from there to Buckingham Palace for a reception with the Queen, Prince of Wales and the Duchess of Cornwall.
The Duke of Sussex will also attend a private lunch at the palace - although his wife, who is on maternity leave, will be at home with their four-week-old son, Archie.
