Foreign secretary Jeremy Hunt has attacked Donald Trump as “disrespectful and wrong” over his extraordinary outburst at Theresa May.

The US President fired off a series of explosive tweets, some of which were aimed at the prime minister, after leaked messages to the UK government by Britain’s US ambassador Sir Kim Darroch suggested his administration was “dysfunctional”. 

May has backed Darroch, saying diplomats should be free to give ministers “unvarnished” advice, but Trump called the ambassador a “pompous fool” and a “very stupid guy” who had been foisted on the US.

He also launched a personal attack on May over Brexit, accusing her of ignoring his advice and “going her own foolish way”.

Tory leadership contender Hunt has now waded into the extraordinary row, warning the president that “allies need to treat each other with respect”. 

He called Trump’s comments about May “disrespectful and wrong” and pointed out that US ambassadors to Britain “give their private opinions” to his administration also. 

Boris Johnson, meanwhile, the frontrunner to replace May, declined to criticise Trump when he was questioned by reporters on the campaign trail in Manchester. 

“I have got a good relationship with the White House and I have no embarrassment in saying that,” he said. 

“I think it’s very important that we have a strong relationship with our most important ally. The United States is, has been, will be and for the foreseeable future our number one political military friend.”

Asked whether the president was right to criticise May and the way Brexit talks have been handled, Johnson replied: “Myself, I have said some pretty critical things about the Brexit negotiations so far and that’s one of the reasons I am standing tonight and one of the reasons I am putting myself forward.

“I think there is a chance to do things differently, a chance to break away from the failed old can-kicking approaching. Now is the time to really get a grip on this. Stop being so defeatist in our approach to the EU negotiations and maybe be a lot more positive about our country and what it can do.”

Trump’s latest intervention came as the cabinet reiterated its full support for Darroch following the leak of a series of diplomatic dispatches in which he branded the US administration as “inept”.

Trump said: “The wacky ambassador that the UK 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 and military anywhere in the world, by far and they are both only getting bigger, better and stronger.

“Thank you, Mr President!”

The war of words comes as the two candidates prepare to debate one another on ITV at 8pm. 

While the prime minister again denounced the leak of Darroch’s dispatches as “unacceptable”, she stressed it was important ambassadors were able to provide “honest, unvarnished” advice to ministers.

“She said we had made clear to the US how unfortunate that this leak is and that the extracts were selective and do not reflect the closeness of our relationship,” the prime minister’s official spokesman said.

“The prime minister said that at the same time – while the views expressed in the documents are not necessarily the views of ministers or the government, it is hugely important that ambassadors are able to provide honest, unvarnished assessments of the politics in their country.

“She said therefore it is absolutely right that we continue to give Sir Kim Darroch our full support.

“The ambassador remains in post and continues to carry out his duties with the full support of the PM.”

The Foreign Office, which originally described the leak as “mischievous”, launched a formal leak inquiry on Sunday.

In the memos, obtained by The Mail On Sunday, Darroch suggested that in order to communicate with the president “you need to make your points simple, even blunt”.

In a scathing assessment of the White House, he said: “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.”