Trump described Johnson as "a very talented guy" for whom he had "a lot of respect".
"I think it's a travesty of British values".
Organizers blasted audio in the direction of the ambassador's house, which they said was a recording of child migrants who had been separated from their parents while trying to enter the United States.
As Trump is expected to discuss a possible post-Brexit trade deal and other global issues with May, organizers of Friday's demonstrations say there is no shortage of issues that will inspire mass numbers of people to attend. Everyone would think he'd gone mad.
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The American president reveals in an interview with The Sun newspaper that he has been told about a 20-foot "Trump baby" balloon that will be flown above Parliament Square on Friday as protesters march.
The two leaders have been highly critical of each other, with Trump going after Khan previous year in the aftermath of a terror attack in London.
Speaking at conclusion of the North Atlantic Treaty Organisation summit in Brussels, Mr Trump gave his views on Britain's withdrawal from the European Union, suggesting it may deliver a softer Brexit against the wishes of the majority of the voting public. You can read terms of service here. Late a year ago, May criticized him for retweeting a message by a member of a British far-right group and the speaker of Britain's parliament has said Trump would not be welcome to address it. Look at what is going on in London.
"I think it changed the fabric of Europe and, unless you act very quickly, it's never going to be what it was and I don't mean that in a positive way".
Trump even appeared to hold Khan personally responsible for immigration in Europe, in comments that were particularly inflammatory.
"The spirit of friendship and cooperation between our countries, our leaders and our people, that most special of relationships, has a long and proud history", she said, adding that the United States was "not just the closest of allies but the dearest of friends".