A leader of the right-wing Oath Keeper militia group “organized an alliance” with the Proud Boys and a third extremist group ahead of the Capitol storming on Jan. 6, according to a new federal court filing.

Kelly Meggs, a self-described leader of the Florida chapter of the Oath Keepers, “plotted with his co-conspirators to stop the certification of the Electoral College vote, prepared to use violence if necessary, and stormed the Capitol,” federal prosecutors said in a Tuesday court filing opposing Meggs’ release pending trial.

The court filing marks the first time prosecutors have offered proof of the various extremist groups working together — a move that suggests the accused rioters linked to the groups may face more serious conspiracy and racketeering charges.

On Dec. 19, the Florida man wrote a Facebook message saying, “This week I organized an alliance between Oath Keepers, Florida 3%ers, and Proud Boys. We have decided to work together and shut this s--- down,” prosecutors said in the 22-page filing.

“Contact with (Proud Boys) and they always have a big group. Force multiplier,” he wrote on Dec. 22.

“We have orchestrated a plan with the proud boys,” Meggs wrote three days later, the feds said.

Meggs also wrote that the Oath Keepers would march with the Proud Boys, “then fall back to the back of the crowd and turn off,” in an apparent suggestion that they were coordinating strategy, according to the feds.

Meggs, of Dunnellon, Florida, was indicted in February and faces conspiracy charges. The new coordination allegations came in a Justice Department memo opposing Meggs’ request to be freed on bail.

Meggs is one of 10 Oath Keepers members charged with playing key roles in the attack on the Capitol, which came as Congress was certifying President Joe Biden’s win over former President Donald Trump.

Meggs helped organize at least 10 online discussions with fellow Oath Keepers members in the month leading up to the Capitol attack. He led and planned the group’s activities and paid for two hotel rooms in Washington, D.C., prosecutors said.

He listed weapons and other things that rioters should bring, including mace, gas masks, batons and body armor, said prosecutors.

Federal authorities have already pointed to the Proud Boys and Oath Keepers as being two of the most prominent instigators of the Jan. 6 siege.

The extremist groups were among the first who breached the outnumbered police lines and forced their way into the building where they tried to hunt down perceived enemies of Trump, prosecutors said.