Donald Trump's re-tweets of far-right group Britain First are a "betrayal of the special relationship", Sadiq Khan has said.
The Mayor of London launched a blistering response to the US President's promotion of three anti-Muslim videos on Wednesday.
"Many Brits who love America and Americans will see this as a betrayal of the special relationship between our two countries," Mr Khan said on Thursday.
"It beggars belief that the President of our closest ally doesn't see that his support of this extremist group actively undermines the values of tolerance and diversity that makes Britain so great."
He said: "As the mayor of this great diverse city, I have previously called on Theresa May to cancel her ill-judged offer of a state visit to President Trump.
"After this latest incident, it is increasingly clear that any official visit at all from President Trump to Britain would not be welcomed.
"The Prime Minister of our country should be using any influence she and her government claim to have with the President and his administration to ask him to delete these tweets and to apologise to the British people."
Mrs May's spokesman said on Wednesday it was "wrong for the President to have done this".
President Trump responded later: "Don't focus on me, focus on the destructive Radical Islamic Terrorism that is taking place within the United Kingdom. We are doing just fine!"
He had come under fire for sharing three anti-Muslim videos posted by Britain First's deputy leader Jayda Fransen.
He re-tweeted the posts to his 43.6 million followers, including unverified footage purporting to show Muslims committing crimes.