Steve Bannon met with Mueller multiple times over the past week

WASHINGTON — Steve Bannon, who served as President Trump's chief strategist, was interviewed by special counsel Robert Mueller over multiple days this week, NBC News has learned from two sources familiar with the proceedings.

Bannon spent a total of some 20 hours in conversations with the team led by Mueller, who is investigating possible collusion between the Trump campaign and Russia as well as other issues that have arisen around the probe.

Bannon left his job as a senior White House adviser in August and returned to a leadership role at Brietbart, the right-wing news site based out of Washington. But he fell out of favor with the site's financial backers, the Mercer family, after criticizing the president and his family in "Fire and Fury," a book about the Trump administration published earlier this year by author Michael Wolff.

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US President Donald Trump (L) congratulates Senior Counselor to the President Stephen Bannon during the swearing-in of senior staff in the East Room of the White House on January 22, 2017 in Washington, DC.

(MANDEL NGAN/AFP/Getty Images)

U.S. President Donald Trump (L-R), is joined by Chief of Staff Reince Priebus, Vice President Mike Pence, senior advisor Steve Bannon, Communications Director Sean Spicer and National Security Advisor Michael Flynn, as he speaks by phone with Russia's President Vladimir Putin in the Oval Office at the White House in Washington, U.S., January 28, 2017. Jonathan Ernst: "Very early in the Trump administration, weekends were as busy as weekdays. On Trump's second Saturday the official schedule said he would be making private phone calls to a number of world leaders including Russia's Vladimir Putin. I arrived early and, before sitting down at my desk walked up to Press Secretary Sean Spicer's office. He, too, was just taking his coat off. I gingerly made the suggestion that previous administrations had sometimes allowed photos of such phone calls through the Oval Office windows on the colonnade. To my mild shock, he didn't even think about it twice. "We'll do it!" he said. In truth, I really only expected the Putin call, but we were outside the windows multiple times throughout the day as the calls went on."

(REUTERS/Jonathan Ernst)

U.S. President Donald Trump talks to chief strategist Steve Bannon during a swearing in ceremony for senior staff at the White House in Washington, U.S. January 22, 2017.

(REUTERS/Carlos Barria)

Trump advisers Steve Bannon (L) and Jared Kushner (R) listen as U.S. President Donald Trump meets with members of his Cabinet at the White House in Washington, U.S., June 12, 2017.

(REUTERS/Kevin Lamarque)

Republican U.S. presidential nominee Donald Trump (C) and campaign CEO Steve Bannon (R) listen to National Park Service Interpretive Park Ranger Caitlin Kostic (2nd R) on a brief visit to Gettysburg National Military Park in Gettysburg, Pennsylvania, U.S. October 22, 2016.

(REUTERS/Jonathan Ernst)

U.S. President Donald Trump (L-R), joined by Chief of Staff Reince Priebus, Vice President Mike Pence, senior advisor Steve Bannon, Communications Director Sean Spicer and National Security Advisor Michael Flynn, speaks by phone with Russia's President Vladimir Putin in the Oval Office at the White House in Washington, U.S. January 28, 2017.

(REUTERS/Jonathan Ernst)

U.S. President Donald Trump signs a memorandum to security services directing them to defeat the Islamic State in the Oval Office at the White House in Washington, U.S. January 28, 2017. Pictured with him are White House senior advisor Steve Bannon (L-R), National Economic Council Director Gary Cohn, Vice President Mike Pence, Deputy National Security Advisor K. T. McFarland, National Security Advisor Michael Flynn, National Security Council Chief of Staff Keith Kellogg and senior advisor Kellyanne Conway.

(REUTERS/Jonathan Ernst)

Trump advisor Steve Bannon (L) watches as US President Donald Trump greets Elon Musk, SpaceX and Tesla CEO, before a policy and strategy forum with executives in the State Dining Room of the White House February 3, 2017 in Washington, DC.

(BRENDAN SMIALOWSKI/AFP/Getty Images)

Senior Advisor Jared Kusher, White House Chief Strategist Steve Bannon and President Donald Trump arrive at the start of a meeting with Senate and House legislators, in the Roosevelt Room at the White House, February 2, 2017 in Washington, DC. Lawmakers included in the meeting were Sen. Orrin Hatch (R-UT), Rep. Kevin Brady (R-TX), Sen. Ron Wyden (D-OR) and Rep. Richard Neal (D-MA).

(Photo by Drew Angerer/Getty Images)

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Bannon appeared Thurday in closed door hearings before the House Intelligence Committee, but the session was brief. Bannon only answered 25 questions and refused to discuss events that took place after the 2016 presidential election, including the transition and his time inside the White House.

Republican chairman Mike Conaway of Texas said after the hearing ended that he would consult with lawyers and House Speaker Paul Ryan about potentially holding Bannon in contempt of Congress.

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