National Security Adviser Michael Flynn answering questions in the briefing room of the White House on Feb. 1. Picture: WIN MCNAMEE/GETTY IMAGES
National Security Adviser Michael Flynn answering questions in the briefing room of the White House on Feb. 1. Picture: WIN MCNAMEE/GETTY IMAGES

WASHINGTON—Federal agents questioned then-National Security Adviser Mike Flynn in January, shortly after the White House denied he had talked about sanctions with a Russian official, according to people familiar with the matter.

The Federal Bureau of Investigation interview, which raises the legal stakes for Mr. Flynn and adds to the political pressure on the White House, came after the president’s spokesman Sean Spicer, at a Jan. 23 news briefing, said Mr. Flynn didn't discuss U.S. sanctions with Sergey Kislyak, Russia’s ambassador to the U.S.

At that point, U.S. intelligence officials had already intercepted conversations between the two men in which they discussed the sanctions, according to people familiar with the matter.

Mr. Flynn’s departure generated more questions Tuesday about what Mr. Trump knew about Mr. Flynn’s activities and why it took weeks for Mr. Trump to push him out.

Mr. Spicer said the president was informed about the contents of Mr. Flynn’s conversations with the Russian ambassador in late January, and White House officials spent a “few weeks” looking into the matter.

Vice President Mike Pence, who had vouched publicly for Mr. Flynn, didn’t learn until Feb. 9 about the discussion of sanctions, said his spokesman, Marc Lotter. Mr. Lotter didn’t explain the lag in the vice president’s knowledge.

It is unclear what Mr. Flynn told the FBI agents, or whether his account during the interview was contradicted by intelligence intercepts. But the very act of undergoing an interview is potentially significant for Mr. Flynn because it is a crime to lie to the FBI; charges have been filed against senior officials in previous administrations for lying to investigators.

Mr. Flynn couldn’t be reached for comment.

The FBI interview underscores that one the most senior officials in the White House had fallen under investigative scrutiny less than a week into Mr. Trump’s presidency.

Mr. Flynn’s contacts with the Russian envoy is one of a number of U.S. counterintelligence investigations into Russian government contacts with people close to Mr. Trump.

Democrats called for congressional hearings to take sworn statements from Mr. Flynn to get to the bottom of what the president knew and when. Republicans began to back some of those calls on Tuesday.

“The [Senate] Intelligence Committee is already looking at Russian involvement in our election,” Senate Majority Leader Mitch McConnell (R., Ky.) said Tuesday. “It’s highly likely they’d want to take a look at this episode as well. They have the broad jurisdiction.”

Rep. Adam Schiff of California, the ranking Democrat on the House intelligence committee, said Tuesday his chief concern was that “the White House evidently knew for some weeks that the country had been misled and they were OK with that. They were willing to labor under this falsehood.”

White House officials defended their handling of Mr. Flynn Tuesday, saying the president moved to push out Mr. Flynn when it became clear that significant questions about his trustworthiness had surfaced.

Mr. Spicer said the president’s eroding level of trust in Mr. Flynn was a result of his contact with the Russian ambassador and a “series of other questionable instances.” Asked Tuesday night to describe the other instances, Mr. Spicer declined to do so.

The sequence of events leading up to Mr. Flynn’s ouster Monday night began on Dec. 29, when the then-President Barack Obama’s administration made public punitive measures against Russia for alleged hacking aimed at meddling with the U.S. presidential election to favor Mr. Trump. The U.S. said it was ejecting 35 suspected Russian intelligence operatives from the country and imposing sanctions on Russia’s two leading intelligence services.

That same day, Mr. Flynn repeatedly reached out to the Russian ambassador, according to people familiar with Russian intercepts. In a call, Mr. Flynn sought to persuade the ambassador not to “overreact’’ to the measures, suggesting Mr. Trump administration’s would soon be able to be more friendly to Russia, these people said.

Word of the contact between the two men first surfaced in mid-January. On Jan. 15, Mr. Pence told CBS that Mr. Flynn never discussed sanctions with the Russian ambassador.

That statement alarmed U.S. intelligence officials, who knew of intercepts showing the two had, in fact, discussed the sanctions, according to people familiar with the discussions. At that point, acting Attorney General Sally Yates, a holdover from Mr. Obama’s administration, discussed the issue with other officials, including FBI Director James Comey, who convinced her to wait a bit longer before alerting the White House, so that their investigation could develop more information, these people said.

A week after Mr. Pence’s statement, The Wall Street Journal reported that U.S. intelligence agencies were investigating communications between Mr. Flynn and Mr. Kislyak. In comments on Jan. 23, Mr. Spicer said the two had discussed four other topics, including a planned phone call between the presidents of the two countries, but not the issue of sanctions.

Some U.S. intelligence officials grew uneasy at the possibility that Russian authorities could, in theory, blackmail Mr. Flynn at some future time by threatening to reveal the true nature of the discussions, these people said. After Mr. Spicer’s public comments about Mr. Flynn on Jan. 23, FBI agents interviewed Mr. Flynn directly about his contacts with the Russian ambassador, these people said.

The FBI interview cleared the way for Ms. Yates to then raise the issue with the White House, officials said. On Jan. 26, she approached Donald McGahn, the White House counsel, about the issue. She warned Mr. McGahn that intercepted communications contradicted Mr. Flynn’s account of the discussions, and that White House officials had conveyed those misstatements to the public.

According to Mr. Spicer, Mr. McGahn quickly took the new information to the president.

After Ms. Yates relayed the concerns, some intelligence officials waited for White House officials to issue a new statement—to correct the public record in some way about Mr. Flynn’s contacts with the ambassador, according to people familiar with the matter. As time went on, it seemed to Justice Department officials that the White House didn’t plan to do so, these people said.

Mr. Trump fired Ms. Yates the Monday after she contacted the White House because she had declined to defend an executive order on refugees and visitors to the U.S.

In a briefing on Tuesday, Mr. Spicer said the president asked for the resignation of Mr. Flynn late Monday because he had lost his trust and confidence after conflicting statements about his communications with Russia’s ambassador to the U.S. Mr. Trump had been evaluating Mr. Flynn’s status ever since the Justice Department informed White House officials that the adviser was misleading them about the content and duration of his contacts, Mr. Spicer said.

Mr. Spicer said that Mr. Trump grew increasingly concerned that Mr. Flynn had misled top administration officials.

“This was an act of trust, whether or not he misled the vice president was the issue,” Mr. Spicer said. He said White House counsel determined during that time frame that Mr. Flynn didn’t violate the law.

Mr. Flynn, a confidant of Mr. Trump’s since his presidential campaign, resigned Monday night, writing that he had “inadvertently briefed” Mr. Pence and other officials “with incomplete information.”

Shortly before his resignation, Mr. Flynn was quoted in the conservative news website The Daily Caller saying his conversation with Mr. Kislyak “wasn’t about sanctions. It was about the 35 guys who were thrown out… It was basically, ‘Look, I know this happened. We’ll review everything.’ I never said anything such as ‘We’re going to review sanctions,’ or anything like that.’’

With Mr. Flynn’s resignation, the White House named Keith Kellogg, the chief of staff at the National Security Council who advised Mr. Trump during the campaign, as acting national security adviser.

—Shane Harris, Byron Tau, Siobhan Hughes contributed to this article.

Write to Devlin Barrett at devlin.barrett@wsj.com and Carol E. Lee at carol.lee@wsj.com

- Wall Street Journal

Please sign in or register to comment.