The FBI arrested three suspected white supremacists on firearms charges on Tuesday, the Justice Department announced Thursday. Brian Lemley, Jr., and William Garfield Bilbrough IV, alleged to be members of "The Base," a racist violent extremist group, were apprehended along with a Canadian national, Patrik Jordan Mathews.

According to a federal official, the men were arrested near Baltimore and were believed to be heading toward Richmond, Virginia, where a pro-gun rally is planned for next week. Lemley has been charged with transporting a machine gun and other firearms charges, and he and Bilbrough have been accused of transporting and harboring "an alien unlawfully present in the United States." Mathews also faces firearms charges.

The FBI alleges Mathews unlawfully crossed from Canada into the U.S. in August. Lemley and Bilbrough, according to the affadavit filed in the case, then drove from Maryland to Michigan to pick up Mathews and bring him back with them to Maryland.

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The affadavit says that in December Lemley and Mathews used firearms parts to make a functioning assault rifle. The two also allegedly tried to produce a hallucinogenic drug, DMT, at Lemley's and Mathews' apartment, and they discussed The Base.

This month, according to the affidavit, Lemley and Mathews bought 1,650 rounds of ammunition and shot the rifle they had made at a gun range in Maryland. They were carrying firearms when they were arrested, apparently while traveling to Richmond.

Among the evidence introduced in court was a photo the government said showed Bilbrough holding a weapon in a recruiting video for The Base.

Screenshot from a recruiting video for the white supremacist group The Base. The Justice Department identified the man at left as William Garfield Bilbrough IV. Court exhibit

According to the Pentagon, Lemley served as a Cavalry Scout specialist in the U.S. Army from August 2004 to December 2007, and he served in Iraq from June 2006 until September 2007.

Mathews is a former Canadian Armed Forces member and was relieved of his duties in August, the Canadian Forces said. The Canadian Broadcasting Corporation reports he was being investigated by officials there for a role in recruiting members for a neo-Nazi extremist group.

Patrik Jordan Mathews Royal Canadian Mounted Police via AP

Mathews joined as a reserve member in 2010 and was a combat engineer at the Canadian Forces Base in Winnipeg. As a reservist, Mathews worked part-time for the military and had no deployments. He never had any access to military weapons or explosives, the Canadian Forces said.

The Canadian Forces said it had been made aware of "possible racist extremist activities" by one of its members in Manitoba before all the media coverage. "The Canadian Forces National Counter Intelligence Unit (CFNCIU) had been investigating the matter for several months," the Canadian Forces press office said. "We would not comment on what prompted or led to this investigation."

Pro-gun groups are planning a rally near the Virginia Capitol next week, on January 20, to protest pending gun control legislation from the Virginia General Assembly introduced by Democrats, who now hold the majority in both chambers of the Virginia legislature.

On Wednesday, after seeing "threats of violence," Virginia Governor Ralph Northam declared a temporary state of emergency banning all weapons, including guns, from Capitol Square ahead of the rally next week.

Former FBI special agent in charge Katherine Schweit said "the threat in this kind of situation is with 1,500 rounds in semi-automatic weapons, hundreds of people could go down in seconds."

One of the rally's organizers, Philip Van Cleave, said Monday's rally should not be canceled because of the three men arrested.

"They're the problem makers, they're trying to create problems, the police will handle them, we will go on. We will not let them deter us or slow us down," Van Cleave said.

Reporting by Andres Triay, Clare Hymes, Jeff Pegues and David Martin. Caroline Linton contributed to this report.