In the wake of President Trump’s unproven claims that Trump Tower was wiretapped, the White House is dealing with fallout from its ally, the U.K.

On Thursday, press secretary Sean Spicer repeated a Fox News report that implicated the U.K. in wiretapping the Trump campaign.

Spicer cited Fox News analyst Andrew Napolitano, who suggested that the British electronic surveillance agency GCHQ had helped former President Obama spy on Mr. Trump before last year’s presidential election.

In a rare statement, the agency has denied those claims, calling them “nonsense” and saying they are “utterly ridiculous and should be ignored.”

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U.K. officials say Spicer has apologized, CBS News White House correspondent Margaret Brennan reports.

The National Security Council said Friday that when British Ambassador Kim Darroch and the British national security adviser, Sir Mark Lyall Grant, expressed their concerns, Spicer and Mr. Trump’s national security adviser, Gen. H.R. McMaster, said Spicer was pointing to public reports and not endorsing a specific story.

Meanwhile, a spokesman for Britain’s prime minister says the White House has promised that it won’t repeat the claims.

Prime Minister Theresa May’s spokesman, James Slack, says the British government has made it clear to the U.S. that the claims should be ignored. He said Friday that Washington has assured Britain they will not be repeated.

The White House on Thursday stood by Mr. Trump’s unproven accusations that his predecessor wiretapped his New York skyscraper.

In angrily defending the president’s statement, Spicer told reporters Mr. Trump “stands by” the four tweets that sparked a firestorm that has threatened Mr. Trump’s credibility with lawmakers. Spicer denounced reporters for taking the president’s words too literally and suggested lawmakers were basing their assessments on incomplete information.

Spicer’s comments were a rebuttal to the top two members of the Senate intelligence committee, who released a statement earlier Thursday declaring there is no indication that Trump Tower was “the subject of surveillance” by the U.S. government before or after the 2016 election. Spicer suggested the statement from Sens. Richard Burr, R-N.C., and Mark Warner, D-Va., was made without a full review of the evidence or, incorrectly, a briefing from the Justice Department.

“They are not findings,” he said.

The standoff between the White House and lawmakers came four days before FBI Director James Comey is slated to testify before Congress, when he will inevitably be asked whether the president’s accusations are accurate. The White House’s refusal to back down raised the stakes for Comey’s appearance before the intelligence committee on Monday.

Mr. Trump tweeted earlier this month that Mr. Obama “was tapping my phones in October” and compared the incident to “Nixon/Watergate” and “McCarthyism.”

Mr. Trump, in an interview Wednesday with Fox News, said he’d learned about the alleged wiretapping from news reports referencing intercepted communications, despite the fact that he and his advisers have publicly denounced stories about government agencies reviewing contacts between Trump associates and Russians.

Mr. Trump said there would be “some very interesting items coming to the forefront over the next two weeks.”

In the two weeks since the tweets, the White House has tried to soften the statement, but has not disavowed it.

Spicer on Thursday asserted that Mr. Trump meant to broadly refer to “surveillance,” rather than a phone wiretap.

“The president’s already been very clear that he didn’t mean specifically wiretapping,” he said.

In an attempt to bolster his case, the spokesman spent nearly 10 minutes angrily reading from news reports which he said pointed to possible evidence of surveillance. The list included a report from The New York Times, which Mr. Trump has dubbed “fake news,” as well as conservative commentary, a little-known blog and several reports based on anonymous sources, which Mr. Trump has said cannot be believed.

It was not immediately clear what prompted the senators’ statements Thursday.

Burr and Warner were among eight senior congressional leaders briefed by Comey on March 10.

“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,” Burr and Warner said in a one-sentence joint statement Thursday afternoon.

The phrasing of the statement left open the possibility that tenants or employees working in the tower may have been monitored. In response to Mr. Trump’s claims and a request from the House intelligence committee, the Justice Department is doing its own review of whether Mr. Trump or any of his associates were the subject of surveillance. The department is slated to provide a response to the committee by Monday.

Burr and Warner are leading one of three congressional investigations into Russia’s interference in the 2016 election, including whether Trump associates were in contact with the Kremlin.

The senators joined a growing, bipartisan group of lawmakers who have publicly disputed Mr. Trump’s accusation in the leadup to Comey’s testimony.

Earlier Thursday, House Speaker Paul Ryan of Wisconsin pushed back on the accusations as well.

“We’ve cleared that up,” Ryan said, adding that he’d received a briefing and had seen no evidence of Mr. Trump’s wiretap claims.

But the issue is unlikely to pass as quickly as some Republicans hope.

Sen. Lindsey Graham, R-S.C., said Thursday that he still believes the FBI or Justice Department should comment publicly in “a simple statement that goes to the heart of the matter - without jeopardizing classified information.”

“I believe such a statement would serve the public well, and I fear that without an official answer this issue will continue to linger,” Graham said in a statement.

On Wednesday, Attorney General Jeff Sessions said he had not given Mr. Trump any reason to believe he was wiretapped by Mr. Obama. Republican Rep. Devin Nunes, chairman of the House intelligence committee, said he had seen no information to support the claim and then went further. He suggested the president’s assertion should not be taken at face value.

“Are you going to take the tweets literally?” Nunes said. “If so, clearly the president was wrong.”