Top US intelligence officials, including the director of the FBI, say they have no information supporting President Donald Trump's claim that his predecessor Barack Obama ordered a wiretap of him during the 2016 election campaign.
FBI Director James Comey appeared on Monday before a panel of Congress members looking into possible intelligence breaches, allegations of Russian hacking, and links between Moscow and Trump's campaign.
"With respect to the president's tweets about alleged wiretapping directed at him by the prior administration, I have no information that supports those tweets," Comey told members of the House Intelligence Committee.
"And we have looked carefully inside the FBI. The Department of Justice has asked me to share with you that the answer is the same ... The department has no information that supports those tweets," he said.
Comey confirmed there is an active investigation looking into alleged Russian interference in the US election.
Russia denies it attempted to interfere in the November 8 presidential vote.
In a separate statement, the White House said on Monday: "There is no evidence of Trump-Russia collusion and there is no evidence of a Trump-Russia scandal".
Michael Rogers, director of the National Security Agency, said he has "seen nothing on the NSA side".
Rogers denied claims made by Trump spokesman Sean Spicer that British intelligence had spied on the Republican candidate, on behalf of President Obama.
"That would be expressly against the construct" of the US agreement with allies on matters of intelligence, he said.
The high-stakes testimony in the House Intelligence Committee - the first public hearing into both controversies - came as Trump sought to steer the news focus by calling the Russia issue, which has been a cloud over his victory, "fake news".
Trump created controversy in early March when he tweeted without giving evidence that Obama's administration had wiretapped Trump Tower in New York City.
The White House went so far last week as to suggest Britain's GCHQ signals intelligence agency cooperated with Obama in the alleged surveillance.
The charge riled the British government and GCHQ, a close ally of US spy agencies, sharply rejected it as "utterly ridiculous".
In his opening statement at the hearing, Republican Representative Devin Nunes issued a similar comment made by Comey, although he said other forms of surveillance of Trump and his associates have not been ruled out.
Al Jazeera's Washington Editor James Bays said the statement by the intelligence officials are "embarrassing" for the Trump administration.
"That's something they don't want to hear in the White House," he said.
Monday's hearing, one of several by congressional panels looking into allegations of Russian meddling, could allow for the greatest public accounting to date of investigations that have shadowed the Trump administration in its first two months.
US intelligence agencies concluded that Russia meddled in the campaign to help Trump defeat Clinton. The FBI has also been investigating ties between Russia and Trump advisers and associates during the campaign.
The Senate Intelligence Committee has scheduled a similar hearing for later in the month.
On Monday, Senate Minority Leader Charles Schumer called on Trump to retract his wiretapping claim "immediately".
"By tweeting this claim and attempting to put unproven theories from the fringes of the American media into the mainstream, President Trump has severely damaged his credibility, which is essential to being president.
"President Trump owes the American people and President Obama more than just an explanation, but an apology. He should admit he was wrong, stop the outlandish tweets, and get to work on behalf of this country," Schumer said.
Source: Al Jazeera and news agencies