FBI Director James Comey Monday offered the most definitive repudiation yet of President Trump's claims that the Obama administration wiretapped the president's New York offices in advance of the 2016 elections.

“The FBI and the Justice Department have no information to support’’ Trump’s wiretap assertions, Comey said.

Comey, appearing before the House Intelligence Committee along with National Security Agency Director Mike Rogers, also confirmed for the first time publicly that the FBI was investigating Russian interference, including communications between Trump associates and Russian officials.

"We're investigating whether there was any coordination between people associated with the Trump campaign and the Russians,'' Comey said, declining to elaborate on whether any such evidence has been uncovered. Comey did acknowledge, however, that the Russians appeared to use a third party--a "cutout''--in its communications with WikiLeaks, which published internal communications in the hack of the Democratic National Committee.

Yet as part of the overall inquiry, Comey and Rogers both said they knew of no evidence that any actual votes during the 2016 election were changed as a result of Russian interference.

Although Trump, as recently as Friday, has continued to defend the extraordinary wiretap allegations that Trump Tower was wiretapped in advance of the 2016 elections, Comey's blunt denial comes after House and Senate leaders have refuted that such surveillance existed in bipartisan joint statements, leaving the White House virtually alone in asserting such claims.

“Let me be clear,'' House Intelligence Chairman Devin Nunes, R-Calif., said Monday, "we know there was not a wiretap on Trump Tower. However, it's still possible that other surveillance activities were used against President Trump and his associates.''

Nunes also said Monday that there is "no evidence to date that officials from any campaign conspired with Russian agents."

California Rep. Adam Schiff, the House committee's ranking Democrat, called Trump's claims ''slanderous,'' adding that "we do not yet know whether the Russians had the help of U.S. citizens, including people associated with the Trump campaign.''

Schiff said that the ongoing effort to determine the scope of Russian interference in the U.S. election system represented the most important challenge for U.S. intelligence.

"The stakes are nothing less than the future of liberal democracy,'' Schiff said.

The false wiretap accusation has not only shadowed the White House for the past three weeks, it also has triggered a diplomatic row with a key ally, as Trump and aides cited a discredited report by Fox News commentator Andrew Napolitano that Obama asked a British intelligence agency to tap Trump. The British government Friday strongly rejected the account and the Trump administration pledged not to use the claim again. Yet asked about the flap during a joint White House appearance with German Chancellor Angela Merkel, Trump appeared to keep the dispute alive, saying: "That was a statement made by a very talented lawyer on Fox, and so you shouldn't be talking to me, you should be talking to Fox. OK?"

On Monday, however, Rogers offered the House panel an unequivocal rejection, saying U.S. authorities never sought the help of British intelligence to conduct such surveillance.

Asked whether the false claims about British intelligence's involvement had damaged the relationship between the U.S. and its primary ally, Rogers said the disclosure was "frustrating.''

Congressional leaders, including several Republicans, have continued to express bewilderment with Trump's continued assertion of the false allegations.

"I don't know the basis for President Trump's assertion,'' Sen. Susan Collins, R-Maine said Sunday. "I do believe he owes us that explanation."

House Speaker Paul Ryan, R-Wis., has also sought to move beyond a dispute that won't seem to go away.

"I want to get on with passing our agenda," Ryan said.

The high-stakes House hearing, part of the larger inquiry into Russia's efforts to influence last year's election, featured numerous efforts to press both Comey and Rogers to disclose either possible targets of the ongoing investigation or issue preliminary conclusions on whether there is any evidence of collusion between Trump associates and Russian officials.

Nunes and former Director of National Intelligence James Clapper have said no such evidence of coordination exists. But Comey and Rogers repeatedly declined Monday to comment on any evidence of collusion.

The FBI director and Rogers also declined numerous times to respond to questions about whether former Trump National Security Adviser Michael Flynn was a subject of the FBI's ongoing inquiry. Flynn was forced to resign last month after it was determined that he misled Vice President Pence about his pre-inaugural contacts with Russian Ambassador to the United States Sergey Kislyak.

Several top Trump advisers' contacts with Kislyak have been called into question, including Attorney General Jeff Sessions who failed to disclose two encounters with the Russian ambassador when questioned during his January confirmation hearing. The disclosure prompted Sessions' recusal from any involvement in the ongoing Russian inquiry.

Committee Republicans suggested Monday that questions about Flynn's contacts with Kislyak only emerged as a result of unauthorized leaks of classified information that later appeared in media accounts. As a result, Rep. Trey Gowdy, R-S.C., and Rep. Tom Rooney, R-Fla., pressed Comey to commit to moving forward with a parallel leak investigation, as it pursued the Russia inquiry.

The committee hearing comes a little more than two weeks after Trump leveled his accusations against Obama in an early Saturday morning tweet-storm. One tweet said: "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!"

The charges brought furious denials from Obama aides, who have asserted that the law forbids presidents from ordering wiretaps.

Trump and aides have also denied any connection to Russians who sought to hack Democratic officials during last year's election and said opponents are leaking derogatory information against them as part of a "witch hunt" to undermine the presidency.

For Comey, Monday's hearing represented another unusually high-profile role for the FBI director.

Comey was harshly criticized by Republicans for the public announcement in July that he was not recommending criminal charges against Clinton for her use of a private email server while secretary of State. He drew the wrath of Democrats in October for announcing that the bureau was reopening its email review, 11 days before the presidential election.

Since Trump made the disputed claims, he and aides have sought to redefine the terms of his accusations. While Trump used the term "wire tapping," he and his aides say that now refers to "surveillance" in general.