Donald Trump's accusation that his office was bugged by the Obama administration during the election campaign has been comprehensively rubbished by the US Congress.
In a statement, Senate Select Committee on Intelligence leaders Richard Burr and Mark Warner said: "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."
But White House spokesman Sean Spicer said on Thursday the US president maintained the allegation, adding: "He stands by it."
Mr Spicer repeated claims, made on Fox News TV by former judge Andrew Napolitano in relation to the wiretap allegations, that British intelligence unit GCHQ had been used to spy on Mr Trump.
In a highly unusual public statement, GCHQ dismissed the claims as "utterly ridiculous".
The spokesman said: "Recent allegations by media commentator Judge Andrew Napolitano about GCHQ being asked to conduct 'wiretapping' against the then president elect are nonsense."
The Senate rebuttal comes two weeks after Mr Trump wrote on Twitter: "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory," and went on to claim nothing was found.
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On Wednesday the leaders of the House Intelligence Committee said they have yet to see any evidence of wiretapping, and House Speaker Paul Ryan insisted that "no such wiretap existed".
The latest and most important denial from the Senate committee follows a claim by the president in a TV interview on Wednesday night that he would "very soon" give further information about what he now says was surveillance and not wiretapping.
"You're going to find some very interesting items coming to the forefront over the next two weeks," he insisted.
The allegations and counter claims about whose phone calls and meetings might have been recorded are becoming increasingly heated in the light of information about links between some of Mr Trump's officials and the Russian government.
In the latest twist it has been revealed that former national security adviser Michael Flynn, who was fired last month by Mr Trump for lying about his connections to the Russian ambassador, was paid more than $33,750 (£27,300) by Russia's state-run broadcaster for giving a speech during the election campaign.
Next week FBI director James Comey and National Security Agency director Mike Rogers will testify before a Congressional committee about what evidence their agencies have about Russia's meddling in the US elections.