FBI Director James Comey says neither the Department of Justice nor his own agency have evidence to support a claim by US President Donald Trump that his Trump Tower headquarters had been wiretapped during the 2016 election 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 a congressional hearing on Monday.
"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 for the Department of Justice and all its components: the department has no information that supports those tweets," he said.
Trump created a controversy in early March when he tweeted without giving evidence that former President Barack Obama's administration had wiretapped Trump Tower in New York.
Comey confirmed the agency was investigating possible Russian government efforts to interfere in the 2016 US election, including any links between Trump's campaign and Moscow.
The probe "includes investigating the nature of any links between individuals associated with the Trump campaign and the Russian government and whether there was any coordination between the campaign and Russia's efforts.
"Because it is an open, ongoing investigation and is classified, I cannot say more about what we are doing and whose conduct we are examining," Comey said.
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US intelligence agencies have concluded that Russia tried to help Trump by hacking leading Democrats' emails. Comey said Moscow had long been opposed to Trump's election rival, former secretary of state Clinton.
"I think that was a fairly easy judgement for the (intelligence) community," he said. "Putin hated Secretary Clinton so much that the flip side of that coin was he had a clear preference for the person running against the person he hated so much."
Trump is keeping tabs on the congressional hearing, tweeting that the FBI and National Security Agency are telling Congress that Russia did not influence the electoral process.
That put Comey in the unusual situation of having to respond to presidential tweets in the middle of his testimony.
Trump's tweet seemed to differ with what Comey said. He told members of the House intelligence committee that the FBI has offered no opinion, and has no view and no information, on the potential impact on the election because that's not something the FBI looked at.
Comey did say earlier in the hearing, however, that there is no evidence that Russian meddling resulted in changes of any vote tallies.
Earlier, the chairman of the US House of Representatives Intelligence Committee, Republican Representative Devin Nunes, told the same hearing that the panel had seen no evidence of collusion between Russia and Trump's 2016 campaign.
Nunes also denied an unsubstantiated claim from Trump that there had been a wiretap on his Trump Tower in New York but said it was possible other surveillance was used against the Republican.
Russia denies it attempted to influence the November 8 presidential election by hacking Democratic operatives and releasing embarrassing information.