Steve Bannon, the former White House chief strategist, was subpoenaed by the investigation into Russian election meddling, The New York Times reported on Tuesday, shortly before he refused to answer questions at a separate panel on the same topic.
Mr Bannon will now be legally obliged to give testimony before a grand jury about the Trump campaign’s links to Russia, according to the paper.
The move was taken by investigators led by Robert Mueller, the special counsel tasked with getting to the bottom of Russia’s involvement in the 2016 US election.
Last week a new book quoted Mr Bannon as saying a meeting attended by Donald Trump’s son, Donald Jr, and Russian-linked figures was “treasonous” and "unpatriotic".
It is believed to be the first time Mr Mueller has used a subpoena – a legal device to force someone to give testimony – since taking over the investigation last year.
The New York Times suggested the move could be a negotiating tactic, with it still possible that Mr Bannon will give evidence to investigators rather than before a grand jury.
Separately, Mr Bannon appeared before the House of Representatives’ Intelligence Committee on Tuesday behind closed doors on the same topic.
He refused to answer a broad array of queries from the House Intelligence Committee about his time working for the President, provoking a subpoena from the panel’s Republican chairman.
Late on Tuesday, Rep. Adam Schiff of California, the top Democrat on the committee, said Mr Bannon’s refusal to answer the questions came at the instruction of the White House.
"This was effectively a gag order by the White House," Mr Schiff said shortly after Mr Bannon’s interview concluded. Mr Schiff said the committee planned to call him back for a second interview.
A spokeswoman for Mr Bannon did not respond to multiple requests for comment Tuesday afternoon.
At the White House, press secretary Sarah Huckabee Sanders said "no one" had encouraged Mr Bannon not to be transparent during questioning but there’s a "process of what that looks like."
"We witnessed today what I believe was the most aggressive effort by the White House thus far to obstruct our efforts to seek the truth."@RepSwalwell reacts to Steve Bannon's refusal to answer questions at the W.H.'s direction during his 9.5-hour under-oath testimony. #LastWord pic.twitter.com/TmUVKm3hXL
Click Here: NRL Telstra Premiership— The Last Word (@TheLastWord) January 17, 2018
"As with all congressional inquiries touching upon the White House, Congress must consult with the White House prior to obtaining confidential material. This is part of a judicially recognized process that goes back decades," Sanders told reporters.
A White House official said the president did not seek to formally exert executive privilege over Mr Bannon – a move that would have barred him from answering certain questions.
Mr Bannon, the former executive chairman at Breitbart News, the right-wing website, was Mr Trump’s election campaign chief for the final few months before the vote.
Profile | Steve Bannon
He is credited with turning round Mr Trump’s fortunes and securing an improbable victory by doubling down on Mr Trump’s nationalistic campaign messages.
However the pair have fallen out spectacularly in the new year after Mr Bannon was quoted at length criticising Mr Trump’s family members in the book Fire and Fury.
In particular, Mr Bannon’s criticism of a controversial Trump Tower meeting between senior campaign aides and Russian-linked figures before the election infuriated the president.
The meeting was set up after Mr Trump’s son was told that the Russians may have dirt on Hillary Clinton, who was running as the Democratic presidential candidate at the time.
Mr Trump publicly attacked Mr Bannon after the comments came to light.
"Steve Bannon has nothing to do with me or my Presidency. When he was fired, he not only lost his job, he lost his mind," he said.