Comey said the investigation is also exploring whether there was any coordination between the campaign and the Kremlin, and "whether any crimes were committed."
The acknowledgment was an unusual move, given that the FBI's practice is not to confirm the existence of ongoing investigations. "But in unusual circumstances, where it is in the public interest," Comey said, "it may be appropriate to do so."
Comey said he had been authorized by the Justice Department to confirm the wide-ranging probe's existence.
He spoke at the intelligence committee hearing along with National Security Agency head Michael S. Rogers.
The committee chairman, Rep. Devin Nunes (R-Calif.), said in his opening statement: "The fact that Russia hacked U.S. election-related databases comes as no shock to this committee. We have been closely monitoring Russia's aggressions for years. . . . However, while the indications of Russian measures targeting the U.S. presidential election are deeply troubling, one benefit is already clear - it has focused wide attention on the pressing threats posed by the Russian autocrat. In recent years, Committee members have issued repeated and forceful pleas for stronger action against Russian belligerence. But the Obama administration was committed to the notion, against all evidence, that we could 'reset' relations with Putin, and it routinely ignored our warnings."
Nunes said he also wants to know if the communications of any campaign officials or associates were subject to any improper surveillance.
"Let me be clear," he said. "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."
In his opening statement, Schiff said: "We will never know whether the Russian intervention was determinative in such a close election. Indeed it is unknowable in a campaign in which so many small changes could have dictated a different result. . . . What does matter is this: the Russians successfully meddled in our democracy, and our intelligence agencies have concluded that they will do so again."
Most important, he said, "we do not yet know whether the Russians had the help of U.S. citizens, including people associated with the Trump campaign. Many of Trump's campaign personnel, including the president himself, have ties to Russia and Russian interests. This is, of course, no crime. On the other hand, if the Trump campaign, or anybody associated with it, aided or abetted the Russians, it would not only be a serious crime, it would also represent one of the most shocking betrayals of our democracy in history."
Just hours before the start of the hearing, Trump posted a series of tweets claiming Democrats "made up" the allegations of Russian contacts in an attempt to discredit the GOP during the presidential campaign. Trump also urged federal investigators to shift their focus to probe disclosures of classified material.
"The real story that Congress, the FBI and all others should be looking into is the leaking of Classified information," Trump wrote early Monday. "Must find leaker now!"
Republican members pressed hard on the subject of leaks to the media that resulted in news stories about contacts between Russian officials and the Trump campaign or administration officials. Nunes sought an admission from the officials that the leaks were illegal under the Foreign Intelligence Surveillance Court act, the law that governs foreign intelligence-gathering on U.S. soil or of U.S. persons overseas.
"Yes," Comey answered. "In addition to being a breach of our trust with the FISA court."
One story in particular that apparently upset the Republicans was a Feb. 9 piece by The Washington Post reporting that Trump's national security advisor, Michael Flynn, discussed the subject of sanctions with the Russian ambassador, Sergey Kislyak, in the month before Trump took office. The Post reported that the discussions were monitored under routine, court-approved monitoring of Kislyak's calls. Flynn, who had denied to Vice President Pence that he had spoken about sanctions, was forced to resign.
Rep. Tom Rooney (R-Fla.) pressed Rogers to clarify under what circumstances it would be legitimate for Americans caught on tape speaking with people under surveillance to have their identities disclosed publicly, and whether leaking those identities would "hurt or help" intelligence collection.
"Hurt," Rogers noted.
Rogers stressed that the identities of U.S. persons picked up through "incidental collection" - that being the way intelligence officials picked up on Flynn's phone calls with Kislyak - are disclosed only on a "valid, need to know" basis, and usually only when there is a criminal activity or potential threat to the United States at play.
Rogers added that there are a total of 20 people in the NSA he has delegated to make decisions about when someone's identity can be unmasked.
Rep Trey Gowdy (R-S.C.) suggested that the leaks were political, stressing that the intelligence community and law enforcement community would not have been helped by the release of such information. He asked Comey if the intelligence community had shared such information with former Attorney General Loretta Lynch, or Obama.
Comey would not comment on his conversations with Obama.
Comey did confirm that the NSA, CIA, FBI, main Justice Department and others - including personnel in the White House in some situations - could have access to unmasked names of U.S. persons.
But he stressed that only the collecting agency can unmask the identities of people. Others with whom the information is shared "can ask the collectors to unmask," he said - but can't do it on their own.
[Intelligence chairman: No evidence for Trump's claim of wiretapping]
The FBI probe combines an investigation into hacking operations by Russian spy agencies with efforts to understand how the Kremlin sought to manipulate public opinion and influence the election's outcome
In January, the intelligence community released a report concluding that Russian President Vladimir Putin wanted to not only undermine the legitimacy of the election process but also harm the campaign of Hillary Clinton and boost Trump's chances of winning.
Hackers working for Russian spy agencies penetrated the computers of the Democratic National Committee in 2015 and 2016 as well as the email accounts of Democratic officials, intelligence official said in the report. The material was relayed to WikiLeaks, the officials said, and the anti-secrecy group began a series of damaging email releases just before the Democratic National Convention that continued through the fall.
On Friday, the Justice Department delivered documents to the committee in response to a request for copies of intelligence and criminal wiretap orders and applications. Nunes, speaking Sunday, said the material provided "no evidence of collusion" to sway the election toward Trump and repeated previous statements that there is no credible proof of any active coordination.
But Schiff, also speaking Sunday, said there was "circumstantial evidence of collusion" at the outset of the congressional investigations into purported Russian election meddling, as well as "direct evidence" that Trump campaign figures sought to deceive the public about their interactions with Russian figures.
The concerns about Moscow's meddling are also being felt in Europe, where France and Germany hold elections this year. "Our allies," Schiff said, "are facing the same Russian onslaught."
