The foreign secretary broke ranks after No 10 – and Boris Johnson – refused to hit back at the US president directly, calling his comments “disrespectful and wrong”.
In a series of tweets directed at Mr Trump, Mr Hunt said: “Friends speak frankly so I will: these comments are disrespectful and wrong to our Prime Minister and my country.”
He went on: “Allies need to treat each other with respect as @theresa_may has always done with you. Ambassadors are appointed by the UK government and if I become PM our Ambassador stays.”
Mr Hunt’s comments came after Mr Trump launched an attack on Sir Kim and prime minister Theresa May over the course of two days.
In a string of posts on Twitter, the US president described Sir Kim as “wacky” and “pompous” and the prime minister’s conduct of Brexit as “foolish” and a “disaster”.
Mr Trump said British diplomat Sir Kim was “not liked or well thought of within the US”, and that the White House “will no longer deal with him”.
The president’s tirade was sparked by emails leaked on Sunday in which Sir Kim described Mr Trump’s administration as “inept” and “dysfunctional”.
Head of the diplomatic service Sir Simon McDonald will appear before MPs on Wednesday to give evidence to the Foreign Affairs Committee following the leaked emails.
MPs have also written to Theresa May, Jeremy Hunt and the Metropolitan Police calling for an investigation into the “serious criminal act”.
Mr Hunt and Boris Johnson, who are vying to succeed Theresa May as prime minister, will go head-to-head in a live TV debate for the first time on Tuesday.
The live debate will take place in front of a studio audience on ITV at 8pm.
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