WASHINGTON — In a double-barreled assault at the White House, FBI Director James Comey on Monday knocked back President Donald Trump’s claim of wiretapping by the Obama administration and disclosed that the FBI is investigating possible “coordination” between Donald Trump’s presidential campaign and Russian authorities.

In a drama-laced House Intelligence Committee hearing carried live for nearly five hours on cable TV, Comey was the most senior U.S. law enforcement official to publicly debunk Trump’s extraordinary charges, first made on Twitter on March 4, that President Barack Obama had wiretapped him at Trump Tower.

“I have no information that supports those tweets and we have looked carefully inside the FBI,” Comey said, adding that the Justice Department and its components also had “no information to support” Trump’s accusation.

But Comey’s rebuke of Trump, which was echoed by Adm. Michael Rogers, director of the National Security Agency, was overshadowed by disclosure of an active counter-intelligence and criminal investigation aimed at the top ranks of the president’s former campaign and potentially the White House.

The FBI is 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,” Comey said.

He said the investigation was undertaken as part of the FBI’s counter-intelligence mission and includes “an assessment of whether any crimes were committed.”

“I can promise you we will follow the facts wherever they lead,” Comey said.

Comey and Rogers refused to say if the FBI investigation, which began last July, had uncovered any evidence of improper collusion or potential crimes, saying it was inappropriate to discuss an ongoing investigation involving classified sources and information.

Even their limited disclosures raised the possibility that some of Trump’s current or former aides could face lengthy investigations and potentially criminal prosecution, however, saddling the White House with a major scandal.

The national security chiefs’ testimony clearly rattled the White House. During the hearing, President Trump tweeted that the FBI and NSA directors had confirmed that “Russia did not influence electoral process.”

That led to an unusual exchange in the House hearing room, when Rep. Jim Himes, D-Conn., asked Comey and Rogers if the president’s tweet had fairly characterized their testimony.

“It certainly wasn’t our intention to say that today because we don’t have any information on that subject,” Comey said carefully.

Earlier Monday, Trump used Twitter to denounce the FBI investigation, as well as separate probes by the GOP-led House and Senate intelligence committees, as “FAKE NEWS,” adding “The Democrats made up and pushed the Russian story as an excuse for running a terrible campaign.”

“There is no evidence of Trump-Russia collusion and there is no evidence of a Trump-Russia scandal,” the White House said later in a statement.

The investigation of a sitting president’s campaign by the FBI raises potentially serious procedural and constitutional issues.

Attorney General Jeff Sessions already has recused himself from overseeing the FBI probe after news reports disclosed he had met twice with Sergey Kislyak, Russia’s ambassador to the United States, during the campaign but failed to tell the Senate during his confirmation hearing.

As a result, Acting Deputy Attorney General Dana Boente will oversee the investigation. If he is confirmed by the Senate as deputy attorney general, Rod Rosenstein would have the last word in the case.

Comey is only four years into his decade-long term. He can be fired by the president, though that surely would draw comparisons to the resignation of President Nixon’s attorney general and the dismissal of the deputy attorney general in the so-called Saturday Night Massacre during Watergate.

Underscoring the delicacy of the situation, Comey repeatedly declined to answer lawmakers’ questions about his investigation, Republicans’ complaints about leaks to the media, or Democrats’ attempts to draw him into a discussion about which Trump aides might be involved.

“I cannot say more about what we are doing,” Comey said.

He also said: “I don’t know how long the work will take.”

Comey and Rogers said they stood by a Jan. 6 report by the U.S. intelligence community that said Russian President Vladimir Putin had approved an intelligence operation in an effort to hurt Democratic nominee Hillary Clinton and to help Trump. They also repeated that U.S. agencies did not try to assess whether the Russian effort, which included hacking of Democratic National Committee computers and leaks of emails that embarrassed the Clinton campaign, had swayed public opinion or affected any votes on Election Day. Both said they were chiefly surprised by the openness of the Russian operation.

“It’s almost as if they didn’t care that we knew what they were doing or that they wanted us to see what they were doing,” Comey said. “It was very noisy, their intrusions in different institutions.”

Republicans on the House committee chiefly focused their questions about leaks of classified information to the media about Trump’s current and former aides, rather than on the probe of Russian meddling.

Few offered any public defense of Trump’s continued claims of wiretapping or of the contacts between his aides and Russian authorities. Several sought to limit the political damage by questioning whether Putin actively sought to help Trump.

David.cloud@latimes.com