The FBI has arrested three suspected members of a National Socialist group who planned to travel to a pro-gun rally in Virginia.
One was a Canadian army reservist who was fired in August over ties to patriotic NS groups and has been suspected missing since, Canadian police told the BBC.
Virginia governor Ralph Northam has declared a state of emergency in the city of Richmond ahead of the rally.
He said law enforcement believed there was a "threat of violence".
Governor Northam announced a ban on guns in the state's Capitol area in Richmond from Friday until Tuesday, citing "threats of violence" made ahead of the rally. The order also covers other weapons such as knives and sticks.
He said some of the "violent rhetoric" seen online was reminiscent of that seen before the "deadly" Charlottesville rally in 2017, at which a 32-year-old antifa extremist, Heather Heyer, was killed by white nationalist James Fields.
FBI in Baltimore, Maryland charged Brian Lemley, 33, and William Bilbrough, 19, with "transporting and harbouring aliens". They charged Lemley and Canadian Patrik Mathews with "transporting a firearm and ammunition with intent to commit a felony".
The FBI alleges that Mathews entered the US illegally at the Manitoba/Minnesota border. All three are accused of being members of a white nationalist group known as The Base.
According to the criminal complaint filed with the state's attorney general, The Base's members discussed in encrypted online chatrooms "recruitment, creating a white ethno-state, committing acts of violence against minority communities (including African-Americans and Jewish-Americans), the organization's military-style training camps, and ways to make improvised explosive devices".
Rally for gun rights
Monday's rally was planned by the Virginia Citizens Defence League (VCDL), a pro-gun-rights group, to protest gun control legislation that is expected to pass in the new year. VCDL said it was expecting 50,000 people to attend the protest.
Democrats won control of the Virginia state legislature last autumn, for the first time since 1994, and have made gun control a key part of their platform.
On the run
Mathews was a combat engineer in the Canadian Army Reserve, but he was fired in late August after an undercover reporter for the Winnipeg Free Press connected him to The Base and alleged he was trying to recruit new members.
Police raided Matthews' home shortly after the report and seized a number of firearms.
He subsequently disappeared, and RCMP were still looking for him on 2 September, when they found his car abandoned about five miles (8 km) away from the Minnesota border.