(CNN) Idaho police officers arrested 31 people Saturday who are believed to be affiliated with the White nationalist group Patriot Front, after they were seen gathering near a Pride parade in the city of Coeur d'Alene, authorities said.
"It is clear to us based on the gear that the individuals had with them, the stuff they had in their possession, the U-Haul with them along with paperwork that was seized from them, that they came to riot downtown," Coeur d'Alene Police Chief Lee White said during a news conference.
The FBI is assisting local police in its investigation, according to FBI Public Affairs Specialist Sandra Yi Barker. Barker said Coeur d'Alene police are the lead law enforcement agency investigating the situation.
The people who were arrested were all wearing similar clothing associated with Patriot Front, including identical insignia, and there was at least one smoke grenade in their possession, police said.
According to the Anti-Defamation League, Patriot Front is a white supremacist group whose members maintain their ancestors conquered America and left it to them. The group split from another white supremacist group, Vanguard America, in late August 2017, per the ADL.
White said the group was equipped with "shields, shin guards and other riot gear with them," along with papers he described as "similar to an operations plan that a police or military group would put together for an event."
The 31 individuals were arrested for conspiracy to riot, which is a misdemeanor, White said, adding the suspects came from at least 11 states.
Coeur d'Alene Mayor Jim Hammond said in a statement that "hate and violence has no place" in the city. All 31 individuals were from outside of the area, Hammond said, adding that the police department "did a great job of staffing for the event to ensure that they could respond to outsiders attempting to cause trouble."
Authorities released mugshots on Sunday of the arrested individuals, all of whom have since posted bond and were released from custody, per the Kootenai County Sheriff's Office. They will be due back in court at a later date.
Among those arrested was Patriot Front leader Thomas Ryan Rousseau, according to Sgt. Shane Moline of the sheriff's office. Rousseau has since bonded out of the Kootenai County Jail.
The North Idaho Pride Alliance released a statement on Sunday, saying, "As a small community nonprofit, North Idaho Pride Alliance is taking a much-needed day of rest after successfully organizing a momentous, joyful, and SAFE Pride in the Park community celebration under the most challenging of circumstances."
The statement continued, "We are deeply grateful to law enforcement agencies who were present and professionally responded throughout the day to keep our community safe."
According to the ADL, Rousseau led several dozen members of Vanguard America Texas during the "Unite the Right" rally in Charlottesville, Virginia, in August 2017.
CNN has reached out to the Patriot Front and people believed to be associated with Rousseau but did not immediately hear back.
The operation in Coeur d'Alene began when a concerned citizen informed police "approximately 20 people jumped into a U-Haul. They had shields and looked like a little army," White said.
There was no violence or significant disruption before the arrests were made, White said, adding, "Today ended up being relatively uneventful overall."
Correction: A previous version of this story incorrectly stated that CNN had reached out to Thomas Ryan Rousseau's legal representative. It's unclear if he has legal representation yet.