The Republican chairman of the US Senate intelligence committee will resign from the post amid an insider trading investigation.
Richard Burr of North Carolina would step down on 15 May, Senate Majority Leader Mitch McConnell said.
It has emerged on Thursday that Mr Burr’s phone has been seized by the FBI as part of the probe.
The senator is alleged to have 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 answered questions from the FBI regarding trades made by her husband, however.
Mr Burr’s office did not respond to a request for comment.
Mr McConnell said in a statement on Thursday: “Senator Burr contacted me this morning to inform me of his decision to step aside as Chairman of the intelligence committee during the pendency of this investigation.
We agreed that this decision would be in the best interest of the committee and will be effective at the end of the day tomorrow.”
Mr Burr, 64, turned over his mobile phone to authorities after federal agents issued and executed a search warrant at his Washington, DC home, the Los Angeles Times first reported.
Senators under fire over virus ‘insider trading’
The seizure marks an escalation into the investigation into Mr Burr launched by the Justice Department begun in March.
Public disclosures first investigated by ProPublica show the senator sold more than 30 stocks between late January and mid-February, including in many sectors now devastated by the coronavirus outbreak, such as hotel, restaurant and shipping industries.
As the chairman of the Senate intelligence committee, Mr Burr receives nearly daily briefings on threats to US national security. Mr Burr has defended the transactions, saying he “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 investigation from the Justice Department, saying it will “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. When this issue arose, Senator Burr immediately asked the Senate Ethics Committee to conduct a complete review, and he will cooperate with that review as well as any other appropriate inquiry,” she said.
The bulk of Mr Burr’s sales occurred on 13 February, just before he 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.