President Trump announced Monday that the U.S. will "no longer deal" with the British ambassador to the United States, after leaked diplomatic cables showed the ambassador secretly slamming Trump in frank and personal terms.

The extraordinary development seemingly rendered Britain's representative to the U.S. a persona non grata for the first time in more than a century. And it came amid reports that the ambassador, Kim Darroch, is actually popular among some White House officials.

"I do not know the Ambassador, but he is not liked or well thought of within the U.S.," Trump wrote on Twitter. "We will no longer deal with him."

On Sunday, Trump called Darroch ineffective and implied he wasn't even worth responding to.

"We’ve had our little ins and outs with a couple of countries, and I would say that the U.K. -- their ambassador has not served the U.K. well, I can tell you that," Trump told reporters. "We are not big fans of that man, and he has not served the U.K. well. So, I can understand it and I can say things about him, but I won’t bother."

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Trump also tweeted Monday: "I have been very critical about the way the U.K. and Prime Minister Theresa May handled Brexit. What a mess she and her representatives have created. I told her how it should be done, but she decided to go another way."

He later added, "The good news for the wonderful United Kingdom is that they will soon have a new Prime Minister. While I thoroughly enjoyed the magnificent State Visit last month, it was the Queen who I was most impressed with!"

Responding to Trump's remarks on Monday, a Downing Street spokesperson said the U.K. has "a special and enduring relationship with the US based on our long history and commitment to shared values and that will continue to be the case."

"'We have made clear to the US how unfortunate this leak is," the spokesperson said. "The selective extracts leaked do not reflect the closeness of, and the esteem in which we hold, the relationship. At the same time we have also underlined the importance of Ambassadors being able to provide honest, unvarnished assessments of the politics in their country. Sir Kim Darroch continues to have the Prime Minister's full support."

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In the leaked documents, Darroch described the Trump administration as "diplomatically clumsy and inept" and said he doubted it would become "substantially more normal."

The memo was one of several documents published by the Mail on Sunday in which Darroch apparently made highly negative statements about the government of Britain's closest ally.

Josh Dawsey, a reporter at The Washington Post, wrote on Twitter that "Trump’s own team likes the ambassador and regularly dines and socializes at the embassy with him."

Added George Conway, the husband of top White House aide Kellyanne Conway and a frequent critic of Trump: "Indeed they do. They never miss parties at the British Embassy. They love the ambassador, as does everyone else (except for a certain narcissist-in-chief). Frankly, the ambassador was being kind in his assessment of the narcissist-in-chief."

International incidents involving British diplomats in the U.S. are rare, but not unprecedented. British ambassdor Lionel Sackville-West was summarily sacked in 1888 for writing the so-called Murchison letter, which touched off a firestorm by indicating that Britain preferred Grover Cleveland over Republican Benjamin Harrison. (Republicans publicized the letter, helping Harrison win the White House.)

And in May 1856, President Franklin Pierce expelled John F. Crampton, then the British ambasador to the U.S., and several other British diplomats, following a lengthy spat over British efforts to recruit North Americans to fight in Crimea.

"It's not entirely unprecedented," Dan Drezner, Professor of International Politics at The Fletcher School of Tufts University, told Fox News. "When WikiLeaks released a trove of diplomatic cables, the Bolivarian leader of Ecuador expelled the U.S. Ambassador. Even in that case, however, the Ecuadoran government went through the proper diplomatic channels. A PNG-by-tweet for the leak of cables confirming mainstream media reporting of the Trump administration is definitely new."

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Over the weekend, Britain's Foreign Office did not challenge the authenticity of the leaked Darroch documents, which covered the period of 2017 to the present, and came to Darroch's defense. It called the leak "mischievous behavior" and said the public has expected diplomats to provide honest assessments of the politics in the countries where they're posted.

The Trump administration has broken from Britain on key issues such as climate change and preventing Iran from developing nuclear weapons.

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The Foreign Office said the leaks would not harm the productive relationship between the British government and the Trump White House. A formal investigation of the leak may be set in motion in the coming days.

It is customary for senior British diplomats posted overseas to file straightforward memos to senior ministers and security services analysts back home so political trends and possible threats to British interests could be gauged, but it's unusual for a large number of them to be made public.

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Justice Secretary David Gauke called the leak "disgraceful" but said Britain "should expect our ambassadors to tell the truth, as they see it."

Trump has not hesitated to inject himself into Britain's political fray, repeatedly criticizing Prime Minister Theresa May's Brexit negotiating strategy and praising both Brexit party leader Nigel Farage and former Foreign Secretary Boris Johnson, a strong contender to become the next prime minister.

Fox News' Lukas Mikelionis and The Associated Press contributed to this report.