Melania Trump dresses
US President Donald Trump (C) and US First Lady Melania Trump (R) walk with US Ambassador to the United Kingdom Woody Johnson (L) as they arrive at the US ambassador's residence Winfield House in London on July 12, 2018.BRENDAN SMIALOWSKI/AFP/Getty Images

US President Donald Trump criticised UK Prime Minister Theresa May's Brexit strategy by saying that her proposals had probably killed off hope of a US trade deal and that she had failed to take his advice on how to negotiate with the European Union.

In an interview with Sun, published just hours before he was due to have lunch with May and tea with Queen Elizabeth, Trump chided the "very unfortunate" results of May's Brexit negotiation.

"If they do a deal like that, we would be dealing with the European Union instead of dealing with the UK, so it will probably kill the deal," Trump told The Sun in an interview published on Friday.

"I would have done it much differently," he told the Sun, which urged its readers to back Brexit before a referendum in June 2016. "I actually told Theresa May how to do it, but she didn't listen to me."

After a tumultuous week for May, when her Brexit Secretary David Davis and Foreign Secretary Boris Johnson resigned in protest at her Brexit plans, Trump heaped praise on Johnson, saying he would be a great Prime Minister. Such harsh public criticism by a sitting U.S. president of a British prime minister while on a visit to the United Kingdom publicly undermines May in her party, her country and abroad.

When asked about Trump's comments, May's spokesman said she was looking forward to sitting down with Trump to talk him through the negotiating stance.

After the story was published, White House spokeswoman Sarah Sanders said the president "likes and respects Prime Minister May very much," adding that he said in the interview she is a very good person, and that he never said anything bad about her.

Melania Trump dresses
US President Donald Trump (2R) and US First Lady Melania Trump (2L) are welcomed by Britain's Prime Minister Theresa May (R) and her husband Philip May (L) as they arrive for a black-tie dinner with business leaders at Blenheim Palace, west of London, on July 12, 2018, on the first day of President Trump's visit to the UK.GEOFF PUGH/AFP/Getty Images

On Thursday, May invoked Winston Churchill as she addressed Trump and business leaders at a black-tie dinner at Blenheim Palace, the 18th-century country house where Churchill was born. "Mr President, Sir Winston Churchill once said that to have the United States at our side was, to me, the greatest joy," May told Trump, according to a text of her speech.

Outside the mansion, northwest of London near Oxford, a couple of thousand demonstrators lined the road and booed Trump's arrival. It was one of more than a hundred protests police expected during Trump's four-day trip.

Trump has frequently angered British politicians. Late last year, 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.

Tens of thousands of British are due to protest on Friday against the visit.