US President Donald Trump has ramped up his criticism of Britain's ambassador, calling him "wacky" and "stupid" in a series of tweets as the row over the leaking of confidential memos continues.

Mr Trump said he had been told Kim Darroch was a "pompous fool" and is not someone the US is "thrilled with".

Yesterday, Mr Trump said he would not deal with Mr Darroch after the leak of memos in which the diplomat described the Trump administration as "inept".

He also said he had advised British Prime Minister Theresa May on how to conduct Brexit negotiations, but "she went her own foolish way - was unable to get it done. A disaster!"

Mrs May's spokesman has said it is her view that Mr Darroch is "a highly respected and dutiful public servant" who "has the full confidence of the prime minister".

The spokesman confirmed that the ambassador is not attending a meeting between Ivanka Trump, an advisor to President Trump, and the UK's International Trade Secretary Liam Fox in Washington.

He also said there are no plans for a phone call between Mrs May and President Trump to discuss relations.

Yesterday, Mrs May's spokesman said while Mr Darroch's opinions did not reflect the view of the government or ministers, he said the diplomat had London's backing and ambassadors needed to have the confidence to give their frank assessments.

"Contact has been made with the Trump administration, setting out our view that we believe the leak is unacceptable," Mrs May's spokesman told reporters.

"It is, of course, a matter of regret that this has happened."

British foreign minister Jeremy Hunt, one of the two contenders to become prime minister, challenged Mr Trump over his criticisms of the British ambassador.

"@realDonaldTrump friends speak frankly so I will: these comments are disrespectful and wrong to our Prime Minister and my country," Hunt said on Twitter today. "Your diplomats give their private opinions to @SecPompeo and so do ours!"

Mr Hunt said if he becomes Prime Minister, the ambassador would remain in his post.