A federal judge sentenced the founder of the far-right militant Oath Keepers Stewart Rhodes to 18 years in prison on Thursday for seditious conspiracy and other crimes related to the US Capitol attack, after a defiant Rhodes stood before him and insisted he is a "political prisoner."

“For decades, Mr Rhodes, it is clear you have wanted the democracy of this country to devolve into violence," US District Judge Amit Mehta said.

"You are not a political prisoner, Mr Rhodes," he said, adding that he believes Rhodes represents an "ongoing threat" to the country.

Rhodes, a former Army paratrooper turned Yale-educated lawyer, was convicted in November by a federal court jury in Washington. Mehta is due to sentence co-defendant Kelly Meggs, a former Florida Chapter leader also convicted of seditious conspiracy, later.

Rhodes' prison term represents the longest sentence for any of the 1,000-plus people charged in connection with the January 6, 2021, Capitol attack by supporters of Republican then-president Donald Trump in a failed bid to block Congress from certifying Democratic rival Joe Biden's November 2020 election victory.

Until now, the longest sentence was 14 years in prison given to a Pennsylvania man who attacked police during the rampage.

Prosecutors had sought a sentence of 25 years for Rhodes.

"Mr. Rhodes led a conspiracy to use force and violence to intimidate and coerce members of our government into stopping the lawful transfer of power following a presidential election,” federal prosecutor Kathryn Rakoczy said. “As the court has just found – that is terrorism.”

Ahead of his sentencing, a defiant Rhodes stood before Mehta, clad in an orange jumpsuit, and insisted that he is a "political prisoner" who, like Trump, was trying to oppose people "who are destroying our country."

“I believe this country is incredibly divided. And this prosecution - not just of me, but of all J6ers – is making it even worse. I consider every J6er a political prisoner and all of them are being grossly overcharged," he said. (Reuters)