WASHINGTON — Republican Sen. Richard Burr temporarily stepped aside as chairman of the Senate Intelligence Committee on Thursday after the FBI served a search warrant for his cellphone as part of an investigation into a well-timed sale of stocks tied to the coronavirus pandemic.

Senate Majority Leader Mitch McConnell announced the move, saying he and Burr had agreed that it was in the committee’s best interests. As he ducked into a Senate Republican lunch, Burr told reporters at the Capitol that he thought it was “the right thing to do.”

“This is a distraction to the hard work of the committee and the members, and I think that the security of the country is too important to have a distraction,” Burr said.

Burr, from North Carolina, said he would serve out the remainder of his term, which ends in 2023. He is not running for reelection.

FBI officials showed up at Burr’s home with the warrant on Wednesday, two people familiar with the investigation said, marking a significant escalation into the Justice Department’s investigation into whether Burr exploited advance information when he unloaded as much as $1.7 million in stocks in the days before the coronavirus caused markets to plummet. The people spoke on condition of anonymity because they were not authorized to discuss an ongoing investigation.

The search warrant was served on a lawyer for Burr, and FBI agents went to the senator’s home in the Washington area to retrieve the cellphone, a senior Justice Department official said. The decision to obtain the warrant, which must be authorized by a judge, was approved at the highest levels of the department, the official said.

Trump, speaking to reporters at the White House before traveling to Pennsylvania on Thursday, said he was unaware that Burr was leaving his intelligence post.

Burr Has Denied Wrongdoing but Has Also Requested an Ethics Review

“I know nothing about it — never discussed it with anybody,” Trump said. “That’s too bad.”

The Justice Department declined to comment. Burr’s attorney did not respond to phone and email messages but said in a statement last month that the law is clear that any senator can participate in stock market trading based on public information “as Sen. Burr did.” The attorney, Alice Fisher, had said that Burr welcomed a review of the stock sales, “which will establish that his actions were appropriate.”

Burr has denied wrongdoing but has also requested an ethics review of the stock sales. His decision Thursday appeared to surprise some members of the committee, where Burr has been a popular chairman and has often worked on a bipartisan basis.

“Oh, wow,” said Sen. Susan Collins, R-Maine, upon learning that Burr had temporarily stepped aside. “I don’t know what to say. I truly didn’t know about it. He’s been an excellent chairman of the committee.”

Texas Sen. John Cornyn, another Republican on the intelligence panel, said he respects Burr’s decision, adding that “he’s entitled to a presumption of innocence just like anybody else.”

“The best I can tell, he is trying to do the right thing by the Senate, and I appreciate it,” Cornyn said.

Senate records show that Burr and his wife sold between roughly $600,000 and $1.7 million in more than 30 transactions in late January and mid-February, just before the market began to nosedive and government health officials began to sound alarms about the virus. Several of the stocks were in companies that own hotels.

Burr has acknowledged selling the stocks because of the coronavirus but said he relied “solely on public news reports,” specifically CNBC’s daily health and science reporting out of Asia, to make the financial decisions.

Senators Received a Closed-Door Briefing on the Virus on Jan. 24

Burr was not the only lawmaker whose stock sales around the same time made headlines.

Republican Sen. Kelly Loeffler, a new senator from Georgia up for reelection this year, sold hundreds of thousands of dollars worth of stock in late January and February, as senators began to get briefings on the virus, according to records. She subsequently said that she would liquidate her stock portfolio and move the money to investment funds after coming under scrutiny for the transactions.

A spokesman for Democratic Sen. Dianne Feinstein of California said Thursday that she was “asked some basic questions by law enforcement about her husband’s stock transactions,” which she voluntarily answered. There has been no follow-up, said the spokesman, Tom Mentzer.

Senators did receive a closed-door briefing on the virus on Jan. 24, which was public knowledge. A separate briefing was held Feb. 12 by the Senate Health, Education, Labor and Pensions Committee, of which Burr is a member. It’s unclear if he attended either session.

He was first elected to the Senate in 2004 and chaired the Senate Intelligence Committee as the panel conducted its own investigation into Russian election interference in the 2016 presidential election. The committee recently issued a report supporting the intelligence community’s conclusion that Russia had interfered on Trump’s behalf.

It’s unclear who will take Burr’s place. The next several Republican members in seniority are already chairmen of other committees, though they could choose to switch.

Next in seniority is Idaho Sen. James Risch, who told reporters on Thursday that he didn’t know if he would keep his current perch as chairman of the Senate Foreign Relations Committee or move to the intelligence panel. Following him is Florida Sen. Marco Rubio, who heads the Senate Small Business Committee. He said that he wasn’t aware that Burr was stepping aside and that the decision on who takes over the panel was up to McConnell. Collins, chairwoman of the Senate Aging Committee, is third in line.

The Los Angeles Times first reported the search warrant.