Correction: An earlier version of this story, published Thursday, incorrectly reported that One America News was warned by the FBI that it was the target of a Russian influence operation. That version also said the FBI had provided a similar warning to Rudolph W. Giuliani, which he has since disputed. This version has been corrected to remove assertions that OAN and Giuliani received the warnings.

The FBI became aware in late 2019 that Rudolph W. Giuliani was the target of a Russian influence operation aimed at circulating falsehoods intended to damage President Biden politically ahead of last year’s election, according to people familiar with the matter.

Officials planned to warn Giuliani as part of an extensive effort by the bureau to alert members of Congress and at least one conservative media outlet, One America News, that they faced a risk of being used to further Russia’s attempt to influence the election’s outcome, said several current and former U.S. officials. All spoke on the condition of anonymity because the matter remains highly sensitive.

The FBI became aware of the Russian information operation at a time when Giuliani was deeply involved with former president Donald Trump’s 2020 reelection campaign and related activities in Ukraine to surface unflattering or incriminating information about the Biden family. The revelation comes as the FBI this week seized Giuliani’s cellphone and other electronic devices as part of a long-running criminal investigation into whether the onetime New York mayor and personal attorney for Trump acted as an unregistered foreign agent.

Andrew Giuliani, son of former New York mayor Rudolph W. Giuliani, on April 28 expressed outrage over federal agents’ search of his father’s Manhattan home. (The Washington Post)

The plan to warn potential targets was separate from the Justice Department’s ongoing criminal probe of Giuliani, but it reflects a broader concern by U.S. intelligence and federal investigators that he — among other influential Americans and U.S. institutions — was being manipulated by the Russian government to promote its interests.

Giuliani traveled in December 2019 to Kyiv, Ukraine’s capital, where he met with a Ukrainian lawmaker whom the U.S. government later labeled “an active Russian agent” and sanctioned on grounds he was running an “influence campaign” against Biden. That operation, officials said, involved Ukrainian officials and political consultants who the U.S. intelligence community has since concluded were acting as Russian proxies not only to smear Biden and derail his candidacy but also to curtail U.S. support for Ukraine.

On Friday, following the initial publication of this report, Giuliani denied he was contacted by the FBI about Russia’s disinformation campaign. One America News President Charles Herring said Friday the network was never contacted by the FBI “regarding Ukraine or people associated with Ukraine.”

An FBI spokeswoman declined to comment.

The FBI last summer also gave what is known as a defensive briefing to Sen. Ron Johnson (R-Wis.), who ahead of the election used his perch as chairman of the Senate Homeland Security and Governmental Affairs Committee to investigate Biden’s dealings with Ukraine while he was vice president and his son Hunter Biden held a lucrative seat on the board of a Ukrainian energy company.

Johnson, a staunch Trump ally, recalled receiving a vague warning from FBI briefers in August, but he said Thursday that there was no substance to their cautionary message and that he did not view the meeting as a “defensive briefing” on his oversight of the Biden family’s foreign business ventures.

“Regarding reports that I received an FBI briefing warning me that I was a target of Russian disinformation, I can confirm I received such a briefing in August of 2020,” Johnson said in a statement to The Washington Post. “I asked the briefers what specific evidence they had regarding this warning, and they could not provide me anything other than the generalized warning. Without specific information, I felt the briefing was completely useless and unnecessary (since I was fully aware of the dangers of Russian disinformation).

“Because there was no substance to the briefing, and because it followed the production and leaking of a false intelligence product by Democrat leaders, I suspected that the briefing was being given to be used at some future date for the purpose that it is now being used: to offer the biased media an opportunity to falsely accuse me of being a tool of Russia despite warnings.”

Johnson and staffers to Sen. Charles E. Grassley (R-Iowa), another Trump ally in the Senate who aided Johnson with his probe, said that in separate briefings earlier in 2020, FBI officials assured them there was no reason to discontinue their inquiry into Hunter Biden’s work in Ukraine. It is not the bureau’s place to tell lawmakers what to investigate or not, or whether to stop or start an investigation, former FBI officials said.

The senators suspected that the younger Biden’s position with the Ukrainian firm posed a conflict of interest to his father’s role shaping U.S. policy toward Ukraine and created impediments for U.S.-backed anti-corruption efforts in that country. Their investigation ended last fall with a report concluding that Hunter Biden’s position with Burisma was “problematic” but did not influence his father’s work or Obama administration policy toward Ukraine.

Defensive briefings are given to people to alert them that they are being targeted by foreign governments for malign purposes, former officials said. But they’re also used “to see how they respond to that,” said Frank Figliuzzi, a former senior FBI counterintelligence official. “They’re now on notice.”

Giuliani’s electronic devices were seized by authorities Wednesday in searches of his Manhattan home and office as part of the federal investigation into whether he acted as an unregistered foreign agent for Ukraine.

The probe centers on Giuliani’s interactions with Ukrainian figures ahead of November’s election, as he sought information that might undermine Joe Biden and lobbied for the ouster of the U.S. ambassador to Ukraine while also pressing Ukrainian officials to announce an inquiry into Biden. Trump abruptly removed the ambassador in May 2019, but Ukraine did not launch an investigation into the Bidens.

Giuliani, a former Manhattan U.S. attorney, has emphatically denied any wrongdoing, and his attorney on Wednesday accused federal investigators of ignoring “clear evidence” of what he alleged was Hunter Biden’s “failure to register as a foreign agent” and the Biden family taking “millions in bribes to sell [Biden’s] public offices.”

Giuliani’s lawyer, Robert J. Costello, has said Giuliani never peddled disinformation on the Bidens.

During his December 2019 trip to Kyiv, Giuliani was accompanied by a team from One America News, which has described itself as one of Trump’s “greatest supporters.” The network later produced a documentary series based on the trip.

The network expressed pride in its investigation of the Bidens in Ukraine.

“We stand by our reporting highlighting Hunter Biden’s financial windfall relationship with Burisma and VP Joe Biden’s efforts to have a Prosecutor General fired to protect alleged wrongdoing by his son, Hunter,” the network said in a statement, referring to unproven allegations made by some Ukrainian officials.

The statement acknowledged that the Treasury Department sanctioned a Ukrainian lawmaker interviewed by the network last year. But, the statement said, “OAN’s interviews were prior to the sanctions and the reasons for sanctions were unknown to OAN at the time of the interviews.”

On his trip to Kyiv, Giuliani met with Andriy Derkach, a politician sanctioned by the United States in September and accused by the Treasury Department of having been an active Russian agent “for over a decade” and maintaining “close connections with Russian intelligence services.” Derkach, who attended a KGB academy in Moscow, has denied involvement with any foreign intelligence agency and any illegal activities.

In late 2019, before Giuliani’s trip to Kyiv, U.S. intelligence agencies warned the Trump White House that Giuliani was the target of a Russian influence operation, as The Post reported last year. Officials became concerned after obtaining evidence, including communications intercepts, that showed Giuliani was interacting with people tied to Russian intelligence. The warnings led then-national security adviser Robert C. O’Brien to caution Trump that any information Giuliani brought back from Ukraine should be considered contaminated by Russia.

Giuliani met with Derkach again in New York in February 2020 when he hosted Derkach on a podcast. In the podcast, Derkach aired false allegations that billions of dollars in U.S. aid to Ukraine were misused or went missing while Joe Biden was handling the Obama administration’s Ukraine portfolio.

Costello has said Giuliani did not rely on Derkach for material.

Since Biden’s victory, the National Intelligence Council, an analytic arm of the Office of the Director of National Intelligence, has concluded that Russian President Vladimir Putin and other senior officials in Moscow sought to influence the 2020 election. They did so by spreading misleading information about Biden through prominent individuals, “including some” who were “close to former President Trump,” according to an ODNI report issued in March.

The report did not identify the individuals by name, but several current and former officials confirmed at the time that Giuliani was among them. The primary narrative that the Kremlin sought to promote — alleging corrupt ties between the Bidens and Ukraine — dated back to at least 2014, the intelligence report said.

To distance themselves from the disinformation, the Russian spy services relied on Ukrainian individuals including Derkach, the report said. Derkach and others “sought to use prominent U.S. persons and media conduits to launder their narratives to U.S. officials and audiences,” the report stated. “These Russian proxies met with and provided materials to Trump administration-linked U.S. persons to advocate for formal investigation . . . and attempted to make contact with several senior U.S. officials.”

Johnson has said he never met or spoke with Derkach. But he and his staff met with another Ukrainian national, former diplomat Andriy Telizhenko, who pushed the unfounded allegation that it was Ukraine rather than Russia that interfered in the 2016 U.S. election. Johnson has not discussed the meeting publicly.

Last year, Sen. Ron Wyden (D-Ore.) alleged that Johnson was seeking to “give credibility” to disinformation advanced by Derkach and Telizhenko “for the sole purpose” of aiding Trump’s reelection. Johnson has said his staff vetted the reliability of Telizhenko’s information and rejected Wyden’s assertion.

As part of his committee’s investigation, Johnson and two Republican colleagues considered subpoenaing Telizhenko to testify. At Senate Democrats’ request, the FBI in March 2020 briefed Johnson’s panel and two other committees on Telizhenko’s background and motives. As a result, both Republican and Democratic lawmakers urged Johnson to refrain from issuing the subpoena.

Telizhenko also has met several times with Giuliani, appearing on his podcast and facilitating his December 2019 trip to Ukraine.

This past January, in the waning days of the Trump administration, the Treasury Department sanctioned Telizhenko as well for his role in trying to influence the 2020 election. He has denied any involvement in Russian interference or disinformation operations and denied working with Derkach.

This month, the Biden administration imposed economic sanctions on 32 entities and individuals for Russian government attempts to influence November’s election.

David L. Stern in Kyiv, and Paul Sonne and Alice Crites in Washington contributed to this report.