A diplomatic rift between the U.K. and the U.S. deepened Tuesday morning as President Trump lashed out at the British government over leaked memos that revealed harsh criticism of the White House by its ambassador to the U.S.

Trump called Ambassador Kim Darroch a “very stupid guy” who was “foisted upon the United States” by the U.K., before reiterating attacks on the “failed Brexit negotiation” of outgoing British Prime Minister Theresa May, who is stepping down after failing to get her government to agree a deal for Britain’s departure from the E.U.

The President claimed he “[doesn’t] know” Darroch, who has served as the U.K.’s ambassador since January 2016, “but [has] been told he is a pompous fool.”

Diplomatic cables written by Darroch were published Sunday in the British paper the Mail on Sunday, covering a period from summer 2017 to last month. “As seen from here, we don’t really believe this administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept,” Darroch wrote in one memo.

The British government has apologized for the leak, calling it “mischievous behavior” and launching an inquiry into how the comments became public.

On Monday, Trump disinvited Darroch from an official dinner hosted by U.S. Treasury Secretary Steven Mnuchin. “We will no longer deal with him,” the President said, casting uncertainty over Darroch’s ability to perform his diplomatic role in Washington.

But May’s spokesman reaffirmed the Prime Minister’s “full support” for Darroch in a statement Monday, saying he would continue his duties as ambassador. The spokesman said it was an ambassador’s job to provide “an honest and unvarnished view” of the situation in countries where they served — though May does not necessarily agree with the content of the memos, he added.

Write to Ciara Nugent at ciara.nugent@time.com.