A MAN pleaded guilty on Thursday to plotting to violently stop the transfer of presidential power after the 2020 US election, making him the first member of the far-right Proud Boys to admit a seditious conspiracy charge.

Jeremy Joseph Bertino, 43, has agreed to co-operate with the Justice Department’s investigation of the role that Proud Boys leaders played in the mob’s attack on the Capitol on January 6, 2021, a federal prosecutor said.

Mr Bertino’s co-operation could ratchet up the pressure on other Proud Boys charged in the siege, including former national chairman Henry “Enrique” Tarrio.

The guilty plea comes as the founder of the another extremist group, the Oath Keepers, and four associates charged separately in the January 6 attack stand trial on seditious conspiracy — a rarely used Civil War era offence that calls for up to 20 years behind bars.

Mr Bertino travelled to Washington with other members of the Proud Boys in December 2020 and was stabbed during a fight, according to court documents. He was not in Washington for the January 6 riot because he was still recovering from his injuries, court papers say.

But Mr Bertino participated in planning sessions in the days leading up to the riot and received encrypted messages as early as January 4 indicating that the Proud Boys were discussing possibly storming the Capitol, according to authorities.

A statement of offence filed in court says that Mr Bertino understood the Proud Boys’ goal in travelling to Washington was to stop the certification of Joe Biden’s victory and that the group was prepared to use force and violence if necessary to do so.

Justice Department prosecutor Erik Kenerson said sentencing guidelines for Mr Bertino’s case recommend a prison sentence ranging from four years and three months to five years and three months.

Members of the Proud Boys describe the group as a politically incorrect men’s club for “Western chauvinists.”

They have brawled with anti-fascist activists at rallies and protests. Vice Media co-founder Gavin McInnes, who founded the Proud Boys in 2016, sued the Southern Poverty Law Centre for labelling it a hate group.