A leader of the Proud Boys and four other members of the far-right group were indicted on sedition charges on Monday in connection with the January 6 assault on the US Capitol.
Henry "Enrique" Tarrio is already facing other charges related to the failed attempt by supporters of former president Donald Trump to block Joe Biden's election victory.
A superseding indictment unveiled on Monday added the more serious charge of seditious conspiracy to the charges against Mr Tarrio, the former "national chairman" of the Proud Boys, and the four other members.
Mr Tarrio was arrested in Miami in March and is also charged with conspiracy to obstruct an official proceeding, obstruction of law enforcement, destruction of government property and other offences.
More than 800 people have been arrested in connection with the storming of Congress by Trump supporters, the Justice Department said, but only a handful face the charge of seditious conspiracy, which carries a sentence of up to 20 years in prison.
Stewart Rhodes, founder of another far-right organisation, the Oath Keepers, has been charged with seditious conspiracy along with 10 other members of the group.
Three members of the Oath Keepers have pleaded guilty.
The superseding indictment said Mr Tarrio was not in Washington on January 6 but he met Mr Rhodes on January 5 in an underground car park in the city, and was in contact with members of the Proud Boys who breached the Capitol.
The four other members of the Proud Boys — Dominic Pezzola, Joseph Biggs, Ethan Nordean and Zachary Rehl — were charged with seditious conspiracy as well as their previous charges.
The indictment comes three days before a public hearing by the House select committee investigating the storming of the US Capitol.
The committee is trying to see if Mr Trump or members of his circle had a role in planning or encouraging the violent attack, and has subpoenaed his advisers and aides.
The assault on the Capitol left at least five people dead and 140 police officers injured, and followed a fiery speech by Mr Trump to thousands of his supporters near the White House.
He was impeached for a historic second time by the House after the Capitol riot — he was charged with inciting an insurrection — but was acquitted by the Senate, where only seven members of his own Republican party voted against him.
