London mayor Sadiq Khan rejected US President Donald Trump's "childish insults," after Trump launched his three-day visit to Britain by calling Khan a "loser."
Tweeting around the time of touchdown at London's Stansted Airport, Trump accused Khan, London's first Muslim mayor, of being "foolishly 'nasty' to the visiting president of the United States, by far the most important ally of the United Kingdom."
"He is a stone cold loser who should focus on crime in London, not me," said Trump, who has had previous Twitter feuds with Khan.
"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," Khan's office said in a statement.
Trump said Khan "reminds me very much of our very dumb and incompetent mayor of [New York City, Bill] de Blasio, who has also done a terrible job - only half his height." De Blasio is widely reported to be 1.96 metres tall.
Khan had given several interviews to British media ahead of the visit, writing in Sunday's Observer newspaper that it was "un-British to roll out the red carpet" to Trump.
He urged Prime Minister Theresa May, who is scheduled to hold talks with Trump on Tuesday, to "issue a powerful rejection - not of the US as a country or the office of the presidency, but of Trump and the far-right agenda he embodies."
