US President Donald Trump and First Lady Melania Trump have arrived in the UK for a three-day state visit.
Air Force One landed at Stansted Airport at around 09:00 BST (04:00 ET).
Mr Trump will meet members of the Royal Family, and is expected to discuss climate change and Chinese technology firm Huawei during talks with outgoing Prime Minister Theresa May.
Minutes before touching down, Mr Trump criticised Mayor of London Sadiq Khan, with whom he has clashed in the past.
He tweeted that Mr Khan – who had earlier said the UK should “not roll out the red carpet” for Mr Trump – was a “stone cold loser”, but the president added he was looking forward to his visit.
Protests are planned in several UK cities during the visit, including London, Manchester, Belfast, and Birmingham.
Mr Trump was greeted by US Ambassador to the UK Woody Johnson and Foreign Secretary Jeremy Hunt.
Tory leadership candidate Mr Hunt, who has spoken about the importance of the UK’s relationship with the US, said Mr Trump mentioned to him “some of his very strong views about the Mayor of London” which he had also tweeted.
Mr Trump’s tweet accused Mr Khan of doing a “terrible job” as mayor, adding: “[He] 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.”
A spokesman for Mr Khan said “childish insults” should be beneath the US president, adding: “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.”
Although Mr Trump has spoken of his admiration for Mrs May, there is expected to be differences of opinion during their talks, which begin on Tuesday.