Donald Trump has hit out at the UK's ambassador to Washington, who said in leaked emails that the Trump administration was "inept".
Emails have emerged from Sir Kim Darroch to the UK government in which he calls the White House "uniquely dysfunctional" and "divided".
Since the candid messages came to light, the US president said his administration were "not big fans" of the ambassador.
"We are not big fans of that man and he has not served the UK well. So I can understand it, and I can say things about him but I won't bother," Mr Trump said.
A formal investigation will be carried out by the Foreign Office into how the messages ended up published in a newspaper.
Among the messages are Sir Kim's scathing assessments of the White House from 2017 to present day.
"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."
He questioned whether the White House "will ever look competent".
International Trade Secretary Liam Fox has called the leak "unprofessional, unethical and unpatriotic" and stressed that the comments were Sir Kim's "personal opinions" and not the views of the British government.
Foreign Secretary Jeremy Hunt said Sir Kim's job was to give "frank reports" but the UK's view was that Mr Trump's administration was "highly effective".