WASHINGTON - Britain on Friday called President Donald Trump’s claims that a British spy agency was involved in wiretapping Trump Tower “ridiculous” and said it received assurances from the White House that the claims wouldn’t be repeated.
A spokesman for British Prime Minister Theresa May called comments made Thursday by White House spokesman Sean Spicer “utterly ridiculous” and said it would be impossible for Britain to spy on a U.S. citizen due to an agreement signed between the two countries.
"We have made this clear to the administration and have received assurances that these allegations will not be repeated," the spokesman said.
The White House later released a statement that said Britain's Ambassador Kim Darroch and diplomat Sir Mark Lyall expressed their concerns to Sean Spicer and national security adviser Lieutenant General H.R. McMaster. It said the Americans explained that Spicer was "simply pointing to public reports, not endorsing any specific story."
WATCH: Trump: 'Should Be Talking to Fox News' on Wiretapping
On Thursday, Spicer cited a Fox News report to back up claims that the British spy agency, known as GCHQ, was involved in wiretapping Trump Tower. Fox host Andrew Napolitano claimed that "three intelligence sources have informed Fox News that President Barack Obama went outside the chain of command" to order the surveillance and that GCHQ was involved.
A spokesman for the GCHQ denied the claims Thursday, saying: "Recent allegations made by media commentator Judge Andrew Napolitano about GCHQ being asked to conduct 'wiretapping' against the then-president elect are nonsense."
The comments came as Spicer faced off with a roomful of reporters who wanted to know why Trump keeps insisting the wiretapping claims are true, even after top lawmakers on the House and Senate intelligence committees say it never happened.
Spicer accused the journalists of "mischaracterizing" what happened in the Senate committee.
He also accused reporters of "cherry-picking" what they choose to cover, and of ignoring House Intelligence Chairman Devin Nunes who said it was "very possible" there was surveillance of Trump.
But Nunes said he does not believe Trump's phones were tapped.
Spicer said Trump put the word "wiretap" in quotes in his original Twitter accusation. Spicer said that means there was widespread surveillance if not actual phone taps.
But the two top senators on the Senate Intelligence Committee, Republican Richard Burr and Democrat Mark Warner, said Thursday: “Based on the information available to us, we see no indications that Trump Tower was the subject of surveillance by any element of the United States government either before or after Election Day 2016.”
Their statement followed one from House Speaker Paul Ryan, who also dismissed the president's explosive claim March 4 that Obama ordered the eavesdropping. "We've cleared that up, that we see no evidence of that," Ryan said.
Trump, however, told Fox News late Wednesday that he "very soon" will produce evidence of Obama's actions. Top leaders of the House Intelligence Committee said Wednesday that Trump's allegation is unfounded, but the president said his administration "will be submitting things" to the panel and that he perhaps will be speaking about his claim next week.
"You're going to find some very interesting items coming to the forefront over the next two weeks," Trump said.
Numerous congressional leaders, both opposition Democrats and Republicans, have sharply rebuked Trump's claim that Obama wiretapped Trump Tower, the New York skyscraper where the billionaire real estate mogul ran his campaign, and his home before winning the White House.
Trump made the wiretapping charge against his predecessor two Saturdays ago in a string of Twitter comments. One of them said: "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory."
Obama dismissed the allegation as "simply false," and Trump since then has not substantiated his claim. Until the Fox interview, Trump dodged reporters' questions about the allegation.
Trump told Fox his Twitter comment "really covers surveillance and many other things. Nobody ever talks about the fact that [the words 'wire tapped'] was in quotes, but that's a very important thing."
On Wednesday, Nunes, who has been supportive of Trump, held a news conference about Trump's wiretapping allegation.
"We don't have any evidence that took place," he said. "I don't think there was a tapping of Trump Tower."
The committee's top Democrat, Congressman Adam Schiff, agreed, saying: "To date, I see no evidence [of Obama having ordered wiretapping], no basis for that whatsoever."
Nunes and Schiff said they are waiting for information from the Department of Justice by next Monday about whether the agency knows of any court-ordered wiretaps of Trump, but said they have learned of no such bugging in their investigation. The congressional probe was requested by the White House after Trump made his wiretapping allegation.
The House Intelligence Committee also is looking at links between Trump campaign aides and Russian officials during the billionaire real estate mogul's long run for the White House, and in the weeks after he won the election.
Nunes said James Comey, director of the Federal Bureau of Investigation, the country's top law enforcement agency, will testify next Monday before the Intelligence Committee about the wiretapping allegation and the agency's investigation of Russian meddling in the election aimed at helping Trump win.
One key U.S. senator, Lindsey Graham of South Carolina, said, "I'm going to get to the bottom of this. Congress is going to flex its muscle."
He vowed, if need be, to subpoena the FBI to determine whether any U.S. judge issued a secret wiretapping order that the FBI carried out.