The Republican chairman of the US Senate intelligence committee will step down while an insider trading inquiry is carried out.
Richard Burr of North Carolina said he had decided to do so because he did not want the investigation to distract the committee from its work.
Mr Burr’s phone has been seized by the FBI as part of the inquiry.
The senator, who denies wrongdoing, allegedly used inside information to avoid market losses from coronavirus.
He and his wife sold as much as $1.7m (£1.4m) of equities in February, just before markets plunged on fears of an economic crisis.
It is illegal for members of Congress to trade based on non-public information gathered during their official duties.
Republican Senators Kelly Loeffler of Georgia and James Inhofe of Oklahoma, as well as Democratic Senator Dianne Feinstein of California, also reportedly sold holdings before the downturn, but are not confirmed to be under investigation.
Ms Feinstein said she had answered questions from the FBI regarding trades made by her husband, however.
Why is Burr stepping back?
Republican Senate Majority Leader Mitch McConnell said Mr Burr had contacted him to inform of his decision to step aside temporarily.
“We agreed that this decision would be in the best interests of the committee and will be effective at the end of the day tomorrow [Friday],” Mr McConnell said in a statement.
Mr Burr said: “The work the Intelligence Committee and its members do is too important to risk hindering in any way. I believe this step is necessary to allow the Committee to continue its essential work free of external distractions.”
He turned over his mobile phone to authorities after federal agents issued and executed a search warrant at his Washington, DC, home.
What are the allegations exactly?
The justice department began investigating Mr Burr, 64, in March.
Public disclosures first investigated by ProPublica show the senator sold more than 30 stocks between late January and mid-February. Some of the stocks were in sectors now devastated by the coronavirus outbreak, such as the hotel, restaurant and shipping industries.
As chairman of the Senate intelligence committee, Mr Burr receives nearly daily briefings on threats to US national security. He defended the transactions, saying he had “relied solely on public news reports” to instruct his decision to sell.
However, he was criticised for publicly downplaying the seriousness of the virus, even as he privately sold equities and warned a private North Carolina business group of the stark risks it posed.
Mr Burr’s lawyer, Alice Fisher, said in March the senator welcomed the justice department investigation because it would “establish that his actions were appropriate”.
“The law is clear that any American – including a Senator – may participate in the stock market based on public information, as Senator Burr did, she said.
The bulk of Mr Burr’s sales occurred on 13 February, just before his speech to the wealthy business constituent group about the dire economic impact of the coronavirus, at a time when the Trump administration was publicly downplaying the threat.
In an audio recording, obtained by US outlet National Public Radio (NPR) he also told the group to curtail their travel. Mr Burr has accused NPR of “misrepresenting” his speech.
Who is Richard Burr?
First elected to the Senate in 2004, he chaired the Senate Intelligence Committee when it investigated Russian election interference in the 2016 presidential election.
The committee endorsed intelligence community findings that Russia had interfered on Donald Trump’s behalf.
Mr Burr’s six-year term ends in 2023 and he does not plan to run for re-election, the Associated Press reports.