Washington - Stewart Rhodes, the founder and leader of the anti-government Oath Keepers militia, was sentenced to 18 years in prison for his role in the violent breach of the U.S. Capitol on January 6, 2021.

Prosecutors wanted 25 years, but the sentence is still the harshest given so far in connection with the January 6 attack by supporters of former president Donald Trump.

Rhodes and a top lieutenant, Kelly Meggs, were convicted in November of seditious conspiracy against the U.S. government by leading the bloody assault while Congress was certifying Joe Biden's electoral victory against Trump.

"You, sir, represent an ongoing threat and peril to this country," Federal Judge Amit Mehta told Rhodes before handing down the sentence. "The moment you are released you'll be prepared to take up arms against your government."

The seditious conspiracy charge accused Rhodes and other Oath Keepers of plotting to use force to "oppose...the authority" of the United States government and to "prevent, hinder, or delay the execution of any law of the United States."

The rarely used Civil War era charge is punishable by up to 20 years in prison.

Lawyers for Rhodes, who has been in detention since his arrest in January 2022, had asked for time served.

A defiant Rhodes took the stand during his sentencing hearing to declare that he is a "political prisoner" and that his "only crime is opposing those who are destroying our country."

He claims that the Oath Keepers, unlike the far-right Proud Boys, was a non-violent group. He said he did not enter the Capitol on January 6 and did not expect other Oath Keepers to breach the building.

But prosecutors say Rhodes, a Yale-educated former Army paratrooper, was the mastermind behind the violent attack.

FILE - A mob of supporters of U.S. President Donald Trump storm the U.S. Capitol building in Washington, Jan. 6, 2021.

Rhodes stood outside the building on January 6 acting like a "general surveying his troops on the battlefield," a prosecutor said during his trial last year.

The Oath Keepers had stationed armed "quick reaction force" teams ready to deploy into the city in support of the assault on the Capitol, prosecutors told the jury.

Federal prosecutor Kathryn Rakoczy said on Thursday that a 25-year sentence was needed to deter others and to uphold the rule of law.

"He's been calling for violent [resistance] to the government for well over a decade," Rakoczy said. "He continues to advocate for political violence."

Rhodes founded the Oath Keepers in 2009. The group sees itself as part of a broader "patriot'' movement that believes that the government is infringing on their rights such as the right to carry firearms.

In recent years, they've spewed anti-immigrant and anti-Muslim rhetoric. Although they disavow violence, several members have been convicted of serious crimes over the past decade.

Judge Mehta said Rhodes, as the Oath Keepers leader, is responsible for the actions of his accomplices.

"He was the reason they were in DC on January 6," Mehta said.

Before Rhodes' sentence, the longest prison term for a January 6 rioter was a little more than 14 years, imposed Pennsylvania welder Peter Schwartz on May 5.

Meggs will be sentenced Thursday afternoon and prosecutors have asked for 21 years in prison.

The Oath Keepers is one of two far-right groups whose leaders have been convicted of seditious conspiracy.

Earlier this month, Proud Boys chairman Enrique Tarrio and three associates were also found guilty of the charge.