A United States man with a loaded handgun, a shotgun and a high-capacity magazine was arrested outside of the site where former president Donald Trump addressed supporters, police announced on Sunday.

The Riverside County Sheriff’s office identified the man who was arrested Saturday as Vem Miller, a 49-year-old resident of Las Vegas, Nevada.

Miller was arrested at a checkpoint “without incident” and booked into the John J Benoit Detention Centre for possession of a loaded firearm and a high-capacity magazine for the handgun.

Police said the incident did not impact Trump’s safety, nor the safety of rallygoers at the Coachella, California venue.

Riverside Sheriff Chad Bianco, who attended Saturday’s rally with his family, told reporters that Miller belonged to the far-right anti-government “Sovereign Citizen” movement. The fringe group denies that any government has authority over them without their explicit consent.

Bianco maintained that sheriff’s deputies prevented a third assassination attempt on the former president.

“I truly do believe that we prevented another assassination attempt, and it was solely by our effort of keeping those types of people out,” Bianco said. “We know that we prevented something bad from happening. And it’s irrelevant what that bad was going to be.”

He did not provide any information on a potential motive.

Multiple passports and driver’s licences were found in Miller’s car when he was stopped at a checkpoint after deputies identified “homemade” licence plates on his car that are typically associated with the sovereign citizen movement, according to Bianco.

A deputy “noticed that the interior of the vehicle was in quite disarray” after the initial stop, he added. Authorities said ammunition for both the handgun and shotgun were found inside the black SUV, which was not registered.

Miller has since been released from custody ahead of trial in state court on the firearms charges. Bianco said any additional charges will be left to federal authorities.

The US Attorney’s Office, US Secret Service and the Federal Bureau of Investigation issued a joint statement in which they said they were aware of Saturday’s arrest, and that “while no federal arrest has been made at this time, the investigation is ongoing”.

Law enforcement has dramatically increased security at Trump’s rallies ahead of November’s election after Trump was shot and lightly wounded while addressing supporters in rural Pennsylvania in July.

A second attempt on his life unfolded in September when authorities apprehended a man outside of his West Palm Beach, Florida golf course that they say camped outside of the facility for 12 hours before Secret Service officers found him with a long rifle poking through a fence on the course’s perimeter.​​​​​​​