Enrique Tarrio, the former chairman of the Proud Boys, and four other members of the far-right group were indicted on Monday for seditious conspiracy in connection with the storming of the Capitol last January, the most serious criminal charges to be brought in the Justice Department’s sprawling investigation of the assault.

The sedition charges against Mr. Tarrio and his co-defendants — Joseph Biggs, Ethan Nordean, Zachary Rehl and Dominic Pezzola — came in an amended indictment that was unsealed in Federal District Court in Washington. The men had already been charged in an earlier indictment filed in March with conspiring to obstruct the certification of the 2020 presidential election, which took place during a joint session of Congress on Jan. 6, 2021.

It was not immediately clear what evidence led to the new charges against the members of the Proud Boys, who were central in the effort to storm the Capitol and help forestall President Donald J. Trump’s defeat.