British officials searched Monday for the source of leaked diplomatic cables in which Britain's ambassador to the United States said President Donald Trump "radiates insecurity" and has an "inept" administration.

International Trade Secretary Liam Fox, who called the leak "malicious" and "unconscionable," told the BBC he intends to apologize to the president's adviser and eldest daughter, Ivanka Trump, when he meets with her Monday as part of a previously scheduled visit.

"I will be apologizing for the fact that either our civil service or elements of our political class have not lived up to the expectations that either we have or the United States has about their behavior, which in this particular case has lapsed in a most extraordinary and unacceptable way," Fox said.

When asked about the leaked memos Sunday, President Trump said Ambassador Kim Darroch "has not served the U.K. well."

"We're not big fans of that man," he said.

'Trump radiates insecurity':UK to investigate leak of ambassador's scathing takes on White House

An investigation into how Darroch's confidential assessments of what he called a "dysfunctional" White House ended up in the hands of a reporter for the British newspaper the Daily Mail is being conducted by civil servants in the Cabinet Office, Prime Minister Theresa May's spokesman, James Slack, said Monday.

Slack said May has "full faith" in Darroch though the prime minister does not share the ambassador's views of Trump or his administration.

May's spokesman said the White House was told that "we believe the leak is unacceptable" and "a matter of regret," according to The Guardian, but he added that it is an ambassador's job to give "honest, unvarnished assessments.”

Foreign Secretary Jeremy Hunt condemned the leak and called for the person behind it to face "very serious consequences" but said Darroch's ability to share his honest opinion is "fundamental" to diplomacy.

"I don't share the ambassador's assessment of either the U.S. administration or relations with the U.S. administration. But I do defend his right to make that frank assessment," Hunt said.

The leaked cables acquired by the Daily Mail spanned a period from 2017 to the present. The most inflammatory statements came from a June 22, 2017, briefing note prepared for senior British officials about the new president and his team.

"For a man who has risen to the highest office on the planet, President Trump radiates insecurity," Darroch wrote in that memo. "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."

In that cable, written a month after Robert Mueller was appointed special counsel to investigate Russian interference in the 2016 election, Darroch said he feared the "worst cannot be ruled out" about potential coordination between the Trump campaign and the Kremlin.

"There could have been active collusion between individuals associated with the Trump campaign and Russian intelligence, especially over the timing of release of hacked emails from inside the Clinton camp," he said. "Dodgy Russian financiers may have bailed out the Trump and Kushner enterprises when both were at risk of bankruptcy in previous decades."

More recently, in a June 22 cable from this year, Darroch called the administration's policy toward Iran "incoherent" and "chaotic" and said he did not expect it to become "coherent any time soon."

Darroch said Trump's explanation that he aborted a military strike against Iran in retaliation for a downed unmanned drone "because of 150 predicted casualties doesn't stand up; he would certainly have heard this figure in his initial briefing." He said it was "more likely that he was never fully on board" over concerns about the potential political fallout.

The ambassador said the "unorthodox" president and his entourage had been "dazzled" during their state visit to Britain and helped fortify relationships with those he called the "Trump Whisperers" who could "ensure the UK voice is heard in the West Wing."

He cautioned that though they considered the trip the "hottest ticket of their careers," the effect could be short-lived because "this is still the land of America First."

Slack said law enforcement would become involved in the investigation into the leak only "if evidence of criminality is found."

Conservative lawmaker Tom Tugendhat, who chairs Parliament’s foreign affairs committee, said he wrote to the chief of London’s Metropolitan Police asking for a criminal investigation into the leak.

Brexit Party leader Nigel Farage said Sunday that the documents made it clear that Darroch was a "globalist" and "completely anti-Trump."

"The sooner he's gone as the U.K.'s ambassador in Washington, the better," Farage said, adding that his assessment had nothing to do with Trump's tweet in 2016 calling for Farage to be the U.K.'s ambassador.

Robin Renwick, who served as Britain’s ambassador to Washington in the 1990s, said the leak made Darroch's position "untenable."

“There will, of course, be a decent interval. He will then have to be moved on,” Renwick told the BBC.

Contributing: The Associated Press