The former leader of the far-right Proud Boys group was arrested on Friday outside the US Capitol, police said.
Enrique Tarrio, who was pardoned by President Donald Trump for his role in the 6 January 2021 riot at the Capitol, was arrested not long after holding a news conference on Friday.
Protesters attempted to drown out the event, held near the site of the riot, but the news conference went on as planned.
In a statement, US Capitol Police said that after the event concluded, a woman put a phone near Tarrio's face, and officers allegedly saw him strike the phone and the woman's arm.
Police said the incident happened as a group, including the Proud Boys, was in the process of leaving the Capitol grounds.
At the news conference, Tarrio was joined by several other group members and by Stewart Rhodes, the leader of the Oath Keepers militia.
Tarrio and other Proud Boys announced plans to sue the US Justice Department.
The group criticised prison conditions and wrongful convictions and said they had used a cryptocurrency to raise funds to launch their lawsuit.
Tarrio was sentenced to 22 years in prison for his role in the Capitol riot. A group of about 200 Proud Boys was at the January 2021 riot, and dozens were arrested and convicted before being released after Trump's blanket pardon, issued on the first day of his second term in office.
