The UK's "wacky" ambassador to the US is "a very stupid guy" Donald Trump has said, amid a row over leaked emails.
This came after Downing Street reaffirmed its "full support" for Sir Kim Darroch.
On Sunday emails revealed the ambassador had called the Trump administration "clumsy and inept".
Sir Kim will now no longer meet the president's daughter Ivanka Trump as scheduled on Tuesday, the BBC has been told.
Mr Trump tweeted: "The wacky Ambassador that the U.K. foisted upon the United States is not someone we are thrilled with, a very stupid guy.
"He should speak to his country, and Prime Minister May, about their failed Brexit negotiation, and not be upset with my criticism of how badly it was handled.
"I told @theresa_may how to do that deal, but she went her own foolish way-was unable to get it done. A disaster!
"I don't know the Ambassador but have been told he is a pompous fool. Tell him the USA now has the best Economy & Military anywhere in the World, by far...and they are both only getting bigger, better and stronger...Thank you, Mr. President!"
Number 10 previously called the leak "unfortunate" and has begun a formal investigation. It said the UK and US still shared a "special and enduring" relationship.
Sir Kim was scheduled to visit the White House alongside International Trade Secretary Liam Fox on Tuesday, but will not now be attending, the BBC's Nick Bryant says.
Confidential emails from the UK's ambassador, leaked to the Mail on Sunday,contained a string of criticisms of Mr Trump and his administration, and said the White House was "uniquely dysfunctional" and divided under his presidency.
Sir Kim, who became ambassador to the US in January 2016 about a year before Mr Trump took office, questioned whether this White House "will ever look competent" but also warned that the US president should not be written off.
The emails, dating from 2017, said rumours of "infighting and chaos" in the White House were mostly true and policy on sensitive issues such as Iran was "incoherent, chaotic".
Speaking on Monday following Mr Trump's initial comments on the leaked emails, Downing Street said the prime minister did not agree with Sir Kim's assessment but had "full faith" in him.
On Tuesday morning, before the president's latest comments, a Downing Street spokesman said: "We have made clear to the US how unfortunate this leak is. The selective extracts leaked do not reflect the closeness of, and the esteem in which we hold, the relationship."
But he said ambassadors needed to be able to provide honest assessments of the politics in their country, and the prime minister stood by Sir Kim.
"The UK 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," he said.
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