Steve Bannon, the former chief strategist to US President Donald Trump, was interviewed by special counsel Robert Mueller for around 20 hours this week, the broadcaster NBC reports.
Bannon spent several days being interviewed by Mueller's team, which is investigating Russian interference in the 2016 election and possible collusion with the Trump campaign, NBC reported.
Bannon, who left the White House in August and had a key role in Trump's campaign team, was also questioned about election interference by the House Intelligence Committee in a closed-door session on Thursday.
However, he refused to answer many questions, only answering 25 which had been pre-approved by the White House, Republican Representative Mike Conaway and Democratic Representative Adam Schiff said.
Bannon reportedly said he been instructed by the White House to invoke executive privilege on Trump's behalf.
"The only questions he would answer were questions that had been scripted, literally scripted for him by the White House," Schiff told reporters after the four-hour session. "That's not how executive privilege works."
Australian Associated Press
