Trump ally Steve Bannon has lashed out at the Biden administration as he surrendered to the FBI to face charges over his refusal to co-operate with the congressional Capitol riot inquiry, reports BBC.
"This is going to be the misdemeanour from hell," the former strategist said outside the FBI's Washington office.
Mr Bannon, 67, faces up to a year in prison and a $100,000 (£75,000) fine if convicted.
He was formally charged on Friday in the case.
Mr Bannon is accused of defying a summons to testify on what he knew about plans for the protest that ended with Trump supporters storming Congress.
Supporters of former President Donald Trump stormed the Congress building on 6 January as results of the 2020 election were being certified inside.
Mr Trump, a Republican, has refused to acknowledge losing the election to Democratic President Joe Biden last year, making claims - without evidence - of mass voter fraud.
Mr Bannon was indicted on one count of refusing to appear for a deposition and one count of refusing to provide subpoenaed documents to a committee investigating the riot.
Appearing outside court on Monday afternoon, he said he believed the charges were politically motivated and vowed to fight them. "We're tired of playing defence. We're going to go on the offense on this," he said.
As part of restrictions set by the court, Mr Bannon will be required to check in weekly, remain at his listed address and notify authorities of any plans to leave the Washington DC area. He was also required to surrender his passport to authorities.
No plea has yet been entered, and a virtual hearing has been scheduled for Thursday morning.
Mr Bannon also live-streamed his arrival for his first court appearance, telling followers: "I want you guys to stay focused, stay on message."
"Remember: Signal not noise. This is all noise, that's signal."
He also urged his supporters to stay focused on taking on what he described as the "illegitimate Biden regime".
According to subpoena documents, Mr Bannon - who currently hosts the right-wing War Room podcast - said on the eve of the riot that "all hell is going to break loose tomorrow".
His lawyers have argued that his communications involving the former president are protected.
Mr Bannon's is the first such indictment to come out of the House of Representatives Select Committee's inquiry of the 6 January events.
Mr Trump has urged former aides to reject deposition requests, arguing that they are covered by executive privilege - a legal principle that protects many White House communications.
Another Trump official, former White House chief of staff Mark Meadows, could also face consequences for defying a similar subpoena to appear before the committee.
Dozens of subpoenas were issued last week, calling on former Trump officials to hand over documents and testify about the riot.
On Sunday, Mr Trump defended his former aide - whom he fired in 2017, saying: "This country has perhaps never done to anyone what they have done to Steve Bannon".