Video report by ITV News' Washington Correspondent Robert Moore
Donald Trump's senior economic adviser has expressed "regret" over Sir Kim Darroch's resignation, but said the UK ambassador's diplomatic cables were "ill-advised".
In the first official US reaction to the resignation of Sir Kim, Larry Kudlow - one of Trump's top advisers - told ITV News the UK ambassador was a "friend of his" and said he will recover from the fallout.
Speaking to ITV News' Washington Correspondent Robert Moore, Mr Ludlow said: “We have a long historical relationship with Britain and that will continue. Kim is a friend of mine. I regret what happened and I’m sure he does too.”
As he entered the West Wing, the adviser - who is known as someone long nurtured by British diplomats and government officials - added: “I’m sorry this happened. Kim will recover. I was surprised. His remarks were ill-advised. Things happen in life. I look forward to getting together with him before he leaves.”
Read more analysis by Robert Moore here.
Meanwhile back in the UK, an inquiry into the leak of diplomatic cables criticising Trump's White House found no evidence of computer hacking and is focusing on whether "someone within the system" was responsible, Sir Alan Duncan said.
Memos from Sir Kim revealed he had criticised the Donald Trump administration, calling it "inept" and "uniquely dysfunctional", leading to his resignation as he said his position had become “impossible” following a barrage of abuse from President Trump.
It comes as Foreign Secretary Jeremy Hunt has failed to rule out Theresa May appointing a new US ambassador before she leaves office, as he says the timing is up to the current prime minister.
However Downing Street has refused to be drawn into the debate whether Mrs May will appoint Sir Kim Darroch's successor.
The prime minister's spokesman said only that a new UK ambassador to the US would be announced "in due course".
"The ambassador is appointed by the Prime Minister on the recommendation of the Foreign Secretary with the approval of the Queen," the spokesman said.
"In terms of this particular replacement, that will take place in due course."
Whereas Mr Hunt said: "The prime minister will now make a decision and its for her and not for people from the sidelines to decide exactly when to appoint a replacement, who the most experienced person is for that role."
He added: "This is a black day for British diplomacy, we have brilliant diplomats, it adds to our strength as a country that we have what many people think is the best diplomatic network in the world.
"I and many staff in the Foreign Office are incredibly dismayed, even angry, about what happened because he [Sir Kim] should have had better support than he had."
Sir Alan also failed to rule out Mrs May choosing the next US ambassador, as he answered an urgent question on the resignation of Sir Kim in the House of Commons today.
Shadow Foreign Office minister Liz McInnes called on the Prime Minister to appoint the next ambassador to prevent her successor from doing so.
She said: "So we still have at least one UK representative willing to speak truth to power in Washington."
Ms McInnes launched an attack on Tory leadership candidate Boris Johnson for failing to defend Sir Kim during the ITV leadership debate and she labelled the former Foreign Secretary "the biggest villain of all."
"He had the chance on Tuesday night, not just once, but six times, to defend Sir Kim and oppose Donald Trump," Ms McInnes said.
"But he took an active choice instead to throw our man in Washington under the bus. It was the most craven and despicable act of cowardice I have seen from any candidate for public office, let alone from someone running to be prime minister."
Liberal Democrat former minister Jo Swinson earlier said Mr Johnson's failure to back Sir Kim suggested the UK could have a prime minister who will be "pushed about by the bully who is President Trump on all sorts of issues".
While Tory MP Roger Gale said Mr Johnson's decision not to back Sir Kim during the debate was "lamentable."
Commons speaker John Bercow backed Sir Kim and his performance as a civil servant, calling him "outstanding."