US 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 into alleged ties between Russia and Mr Trump's 2016 presidential campaign, according to the New York Times.
- Robert Mueller subpoenas Steve Bannon to testify before grand jury on Russia
- Mr Bannon is first of Mr Trump's inner circle to be called to give evidence in probe
- Separately, Mr Bannon testified before Intelligence Committee this week on Russia
It was the first time Mr Mueller is known to have used a subpoena against a member of Mr Trump's inner circle, the Times said.
A spokesman for Mr Mueller's office declined to comment.
Bill Burck, a lawyer for Mr Bannon, could not immediately be reached for comment.
Mr Bannon, a champion of Mr Trump's "America First" agenda, was among the Republican's closest aides during the 2016 election campaign, the presidential transition and during his first months in office.
But the pair had a bitter public falling out over comments Mr Bannon made to author Michael Wolff for his recent book, Fire and Fury: Inside the Trump White House.
In the book, Mr 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 candidate Hillary Clinton, to which he replied: "I love it."
Mr Bannon was fired by the White House in August and returned to the right-wing news website Breitbart News.
He continued to speak with Mr Trump and tried to promote the president's agenda.
But Mr Trump accused Mr Bannon of having "lost his mind" when news of his comments to Wolff surfaced earlier this month.
Six days later, Mr Bannon stepped down from his post as executive chairman at Breitbart News.
Mr Mueller's subpoena, which was issued last week, could be a pressure tactic to induce Mr Bannon to cooperate fully with his investigation, the Times reported.
Bannon testifies before Intelligence Committee
Separately on Tuesday, Mr Bannon was meeting with the House of Representatives Intelligence Committee.
He was the latest high-profile figure to testify before the panel as part of its investigation into Russian interference in the US election.
Russia has denied meddling in the election and Mr Trump has denied there was any collusion between his campaign and Moscow.
Later in the week, the panel will hear from former Mr Trump's campaign manager Corey Lewandowski.
White House communications director Hope Hicks, who served as Mr Trump's spokeswoman during his presidential campaign after a tenure with his Trump Organisation 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 witness.
Republicans have denied the charge.