US President Donald Trump arrived in the UK on Monday for a three-day state visit and set a combative tone by attacking London Mayor Sadiq Khan, with whom he has clashed in the past, as his plane landed.
After Air Force One touched down at the Stansted Airport, the President and his wife, First Lady Melania, were greeted by Foreign Secretary Jeremy Hunt.
Trump was seen chatting with Hunt for a minute and occasionally patting him on the back.
Minutes before touching down, Trump tweeted that Khan, who said on Sunday that the US President was like a 20th-century fascist and also suggested that the UK should "not roll out the red carpet", was a "stone cold loser".
"@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been 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," he said in the tweet.
Trump compared Khan to "our very dumb and incompetent" New York Mayor Bill de Blasio, "who has also done a terrible job".
But Trump added that he was still looking forward to his visit, reports the BBC.
Trump's agenda on Monday includes a tour of Westminster Abbey. He will also meet Prince Charles and the Duchess of Cornwall for tea at Clarence House.
In the evening, Queen Elizabeth II will host a state banquet at Buckingham Palace for the Trumps, where they will be joined by the Duke and Duchess
of Cambridge. Meghan Markle, the Duchess of Sussex will not attend following the birth of her son Archie, who is less than a month old.
On Tuesday, Trump and outgoing Prime Minister Theresa May will host a business breakfast at St James's Palace after which they then visit Downing Street for further talks, followed by a joint press conference.
But Hunt indicated on Monday that Trump and May might not have a one-to-one discussion during meetings on Tuesday. "He's going to sit down with Theresa May in a meeting which I will be at, and he may well sit down with her one-to-one, as often happens, before or after those meetings."
The two leaders are expected to discuss climate change and Chinese technology firm Huawei.
Before the visit, Trump told the Sun newspaper that he was backing Conservative Party leadership contender Boris Johnson to be the next Prime Minister.
He also told the Sunday Times that Brexit Party leader Nigel Farage - an arch critic of May - should be involved in the government's negotiations to leave the European Union.
Meanwhile, tens of thousands of protesters are expected to take to the streets across the UK, including in London, Manchester, Belfast and Birmingham to demonstrate against Trump's visit.
On Wednesday, Trump will visit Portsmouth to mark the 75th anniversary of the D-Day landings.
He will then fly to Shannon, in Ireland, to meet Prime Minister Leo Varadkar, before going to his golf course at Doonbeg in County Clare.