WASHINGTON — FBI Director James Comey confirmed Monday that the bureau is investigating possible links and coordination between Russia and associates of President Donald Trump as part of a broader probe of Russian interference in last year’s presidential election.

The extraordinary revelation came at the outset of Comey’s opening statement in a congressional hearing examining Russian meddling and possible connections between Moscow and Trump’s campaign. He acknowledged that the FBI does not ordinarily discuss ongoing investigations, but said he’d been authorized to do so given the extreme public interest in this case.

“This work is very complex, and there is no way for me to give you a timetable for when it will be done,” Comey told the House Intelligence Committee.

Earlier in the hearing, the chairman of the committee contradicted an assertion from Trump by saying that there had been no wiretap of Trump Tower. But Rep. Devin Nunes, a California Republican whose committee is one of several investigating, said that other forms of surveillance of Trump and his associates have not been ruled out.

Comey was testifying at Monday’s hearing along with National Security Agency Director Michael Rogers.

Trump, who recently accused President Barack Obama of wiretapping his New York skyscraper during the campaign, took to Twitter before the hearing began, accusing Democrats of making up allegations about his campaign associates’ contact with Russia during the election. He said Congress and the FBI should be going after media leaks and maybe even Hillary Clinton instead.

“The real story that Congress, the FBI and others should be looking into is the leaking of Classified information. Must find leaker now!” Trump tweeted early Monday as news coverage on the Russia allegations dominated the morning’s cable news.

WATCH: House intelligence committee hearings on Russia and the 2016 election

Trump also suggested, without evidence, that Clinton’s campaign was in contact with Russia and had possibly thwarted a federal investigation. U.S. intelligence officials have not publicly raised the possibility of contacts between the Clintons and Moscow. Officials investigating the matter have said they believe Moscow had hacked into Democrats’ computers in a bid to help Trump’s election bid.

Monday’s hearing, one of several by congressional panels probing 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.

The top two lawmakers on the committee said Sunday that documents the Justice Department and FBI delivered late last week offered no evidence that the Obama administration had wiretapped Trump Tower, the president’s New York City headquarters. But the panel’s ranking Democrat said the material offered circumstantial evidence that American citizens colluded with Russians in Moscow’s efforts to interfere in the presidential election.

“There was circumstantial evidence of collusion; there is direct evidence, I think, of deception,” Rep. Adam Schiff, D-Calif., said on NBC’s “Meet the Press.” ”There’s certainly enough for us to conduct an investigation.”

Nunes said: “For the first time the American people, and all the political parties now, are paying attention to the threat that Russia poses.”

“We know that the Russians were trying to get involved in our campaign, like they have for many decades. They’re also trying to get involved in campaigns around the globe and over in Europe,” he said on “Fox News Sunday.”

The Senate Intelligence Committee has scheduled a similar hearing for later in the month.

It is not clear how much new information will emerge Monday, and the hearing’s open setting unquestionably puts Comey in a difficult situation if he’s asked to discuss an ongoing investigation tied to the campaign of the president.

At a hearing in January, Comey refused to confirm or deny the existence of any investigation exploring possible connections between Trump associates and Russia, consistent with the FBI’s longstanding policy of not publicly discussing its work. His appearances on Capitol Hill since then have occurred in classified settings, often with small groups of lawmakers, and he has made no public statements connected to the Trump campaign or Russia.

Any lack of detail from Comey on Monday would likely be contrasted with public comments he made last year when closing out an investigation into Clinton’s email practices and then, shortly before Election Day, announcing that the probe would be revived following the discovery of additional emails.