Washington DC - Four members of the far-right group the Proud Boys on Thursday were convicted for seditious conspiracy related to the attack on the US Capitol in January 2021, the Department of Justice said.

A jury in Washington found group leader Henry "Enrique" Tarrio and three other men guilty, among other things, of "seditious conspiracy" in connection with the January 6 attack.

The four defendants and a fifth member of the Proud Boys were also convicted of felonies including obstructing the US Congress's certification of the 2020 presidential election results and conspiring to prevent Congress and federal officers from discharging their duties.

"Today's verdict makes clear that the Justice Department will do everything in its power to defend the American people and American democracy," US Attorney General Merrick Garland said in a statement.

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The sentencing will be determined at a later date. The charge of seditious conspiracy, which has been used very rarely in the country's judicial history, carries a maximum sentence of 20 years.

In recent months, several members of the extreme right-wing group Oath Keepers have also been convicted of seditious conspiracy.

On January 6, 2021, supporters of then US president Donald Trump violently stormed the US Congressional seat in Washington, where the Republican's election defeat to US President Joe Biden was to be certified at the time.

A crowd incited by Trump, who held a rally to promote baseless claims of election fraud, violently entered the building, killing five people.

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"Since the January 6th attack, the Justice Department has conducted one of the largest, most complex, and most resource-intensive investigations in our history," Garland said.

"Over the past two years, the Department has secured more than 600 convictions for a wide range of criminal conduct on January 6th, as well as in the days and weeks leading up to the attack," he added. "Our work will continue."