President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in a tweet early Monday called London Mayor Sadiq Khan a "stone cold loser" ahead of the president's visit to the city.

".@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," Trump tweeted.

"He is a stone cold loser who should focus on crime in London, not me," he added.

.@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...... — Donald J. Trump (@realDonaldTrump) June 3, 2019

Trump followed up with a second tweet likening Khan to another one of his American rivals — New York City mayor and Democratic presidential candidate Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE. Both are "very dumb and incompetent," he said.

He made a similar dig at Khan while speaking to reporters outside the White House Sunday before leaving for his Europe trip, saying he thinks Khan is de Blasio's "twin ... except shorter."

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Khan wrote a fiery op-ed on Saturday that the United Kingdom is on the “wrong side of history” ahead of Trump's visit.

“In years to come, I suspect this state visit will be one we look back on with profound regret and acknowledge that we were on the wrong side of history,” Khan said in The Guardian.

Trump's visit to England comes as the nation is divided in still undecided Brexit negotiations and searching for a prime minister. Trump has publicly supported the controversial conservative choice Boris Johnson, saying he would be "excellent."

Trump on Sunday also pushed back on reports that he called Meghan Markle Meghan MarkleTrump wishes Prince Harry 'luck' with Meghan Markle after Biden endorsement: 'Not a fan' Meghan Markle and Prince Harry call on voters to 'reject hate speech' and 'misinformation' Does Kamala Harris's music matter? MORE, Duchess of Sussex, "nasty."

"I never called Meghan Markle 'nasty,' " he said.

"Made up by the Fake News Media, and they got caught cold!" he added. "Will @CNN, @nytimes and others apologize? Doubt it!"

The president said in an interview published last week that he was not aware that Markle had called him “divisive” and “misogynistic” during his 2016 presidential campaign.

“I didn’t know that. What can I say?” he told The Sun.

“I didn’t know that she was nasty,” he added.