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," Mr Comey told a congressional hearing on Monday (local time).
"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."
Mr 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.
Mr Comey confirmed the agency was investigating possible Russian government efforts to interfere in the 2016 US election, including any links between Mr 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," Mr Comey said.
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.
Other congressional committees also are investigating the possible Russian connection, mostly behind closed doors.
Amid a furore over whether Moscow tried to influence the presidential race on Mr Trump's behalf to the detriment of Democrat Hillary Clinton, lawmakers said they would make public as much of their investigations as possible.
Russia denies it attempted to influence the November 8 presidential election by hacking Democratic operatives and releasing embarrassing information.