US Attorney General Jeff Sessions has been questioned by investigators examining whether Russia colluded with the Trump campaign in the 2016 election.
A Department of Justice (DOJ) spokeswoman confirmed to the BBC the attorney general was interviewed last week.
Mr Sessions appears to be the first member of President Donald Trump's cabinet to be questioned.
Former FBI Director Robert Mueller is leading the inquiry into alleged Russian meddling in the 2016 election.
Mr Mueller, who was appointed as special counsel, is also investigating whether Mr Trump's firing of FBI director James Comey last year was an effort to obstruct the agency's Russia probe.
The interview with Mr Sessions, the nation's top lawman, lasted several hours, according to US media reports.
The US intelligence community has already concluded that Moscow tried to sway the presidential election in favour of Mr Trump, though Russia denies this.
Special Counsel Mueller, as well as three different congressional committees, are investigating the allegation of Russian meddling, and possible collusion.
Mr Sessions, who oversees the FBI at the DOJ, recused himself from the investigation in March 2017 after he acknowledged two previously undisclosed meetings with a Russian ambassador during the campaign.
The president repeatedly criticised Mr Sessions for his recusal on Twitter.
The former Alabama senator could be an important witness due to his ties to the firing of Mr Comey.
The White House initially said that the FBI director's sacking was on the recommendation of the justice department, citing a DOJ memo faulting Mr Comey for his handling of the investigation into Hillary Clinton's use of a private email server.
But Mr Trump later said he was thinking of "this Russia thing" when he fired Mr Comey.
The revelation comes a day after news website Axios reported that FBI Director Christopher Wray threatened to resign after he was allegedly pressured by Mr Sessions to fire his deputy, Andrew McCabe.
Mr McCabe served as acting FBI director before the president tapped Mr Wray to replace Mr Comey.
Mr Trump has criticised Mr McCabe for the FBI investigation into Mrs Clinton's use of a private email server, pointing out that his wife ran for Virginia state office as a Democrat during the inquiry.
Former Governor Terry McAuliffe, a Clinton ally, donated to his wife's failed campaign, but the FBI concluded earlier this month that Mr McCabe had no conflicts in the Clinton investigation.
In response to the Axios report, White House spokesman Raj Shah said that Mr Trump "believes politically-motivated senior leaders including former Director Comey and others he empowered have tainted the agency's reputation for unbiased pursuit of justice".
"The President appointed Chris Wray because he is a man of true character and integrity, and the right choice to clean up the misconduct at the highest levels of the FBI," he added.