President Donald Trump's former chief strategist Steve Bannon has been subpoenaed by Special Counsel Robert Mueller to testify before a grand jury in a probe of alleged ties between Russia and Trump's 2016 presidential campaign, the New York Times reported Tuesday.
It was the first time Mueller is known to have used a subpoena against a member of Trump's inner circle, the Times said. It cited a person with direct knowledge of the matter.
A spokesman for Mueller's office declined comment. Bill Burck, a lawyer for Bannon, could not immediately be reached for comment.
The reported subpoena of Bannon does not mean he is a target of Mueller's criminal investigation.
Bannon, a champion of Trump's "America First" agenda, was among the Republican's closest aides during the 2016 election campaign, the presidential transition and his first months in office.
But the pair had a bitter public falling out over comments Bannon made to author Michael Wolff for his recent book Fire and Fury: Inside the Trump White House.
In the book, Bannon is quoted as describing a June 2016 meeting between Trump associates, including the president's son Donald Trump Jr., his son-in-law, Jared Kushner, and a Russian lawyer, as "treasonous" and "unpatriotic."
The meeting came after Donald Trump Jr. was told in an email that the Russian government had compromising information about Democratic presidential nominee Hillary Clinton, to which he replied: "I love it."
Russia has denied meddling in the election and Trump has denied any collusion between his campaign and Moscow.
Bannon was fired by the White House in August and returned to the right-wing news website Breitbart News. He continued to speak with Trump and tried to promote the president's agenda.
But Trump accused Bannon of having "lost his mind" when news of his comments to Wolff surfaced earlier this month. Six days later, Bannon stepped down as executive chairman at Breitbart.
Mueller's subpoena, which was issued last week, could be a pressure tactic to induce Bannon to cooperate fully with his investigation.
Attorney Renato Mariotti, a former federal prosecutor, said the most likely reason for a Mueller subpoena of Bannon was that "he thought having an attorney present and giving Bannon a more relaxed setting would not yield the same testimony as if he got him in the grand jury room with no attorney there and a more adversarial style of questioning."
A witness is not permitted to bring an attorney into a federal grand jury proceeding, but can step outside to consult with counsel.
Separately on Tuesday, Bannon spent hours meeting behind closed doors with members of the House of Representatives Intelligence Committee. He was the latest high-profile figure to appear before the panel as part of its investigation into allegations of Russian interference in the U.S. election.
After Bannon refused to answer questions about his time in the White House — as opposed to during the campaign — Devin Nunes, the committee's Republican chairman, authorized a subpoena during the meeting to press Bannon to respond.
"Of course I authorized the subpoena. That's how the rules work," Nunes told reporters.
Asked if the White House had told Bannon not to answer certain questions, spokeswoman Sarah Huckabee Sanders said: "As with all congressional activities touching upon the White House, Congress must consult with the White House prior to obtaining confidential material."
"We've been cooperating fully with these ongoing investigations and encourage the committees to work with us to find an appropriate accommodation in order to ensure Congress obtains information necessary to its legitimate interests," she said.
Later in the week, the panel will hear from former Trump campaign manager Corey Lewandowski.
White House Communications Director Hope Hicks, who served as Trump's spokeswoman during his presidential campaign after a tenure with his Trump Organization real estate business, is also expected to be questioned by the committee this week, according to a congressional source.
Democrats on the committee have accused Republicans of rushing to wrap up the probe to help give the president political cover, despite their requests to interview more witnesses. Republicans have denied the charge.