Open this photo in gallery A U.S. district court document image of Patrik Mathews, a former Canadian Armed Forces reservist, seen during a video where he is espousing violent, anti-Semitic and racist language while wearing a gas mask and disguising his voice. AEly/Courtesy of manufacturer

A former Canadian Forces reservist accused of being a violent neo-Nazi was recorded talking about wanting to incite a U.S. civil war at a pro-gun protest in Virginia, newly released U.S. court documents allege.

The documents, which prosecutors filed on Tuesday, are based on Federal Bureau of Investigation intercepts of conversations in December at the Delaware apartment Patrik Mathews shared with a co-accused.

Mr. Mathews was arrested last week with two other men. They are charged with unlawfully transporting an assault rifle and ammunition with intent to commit a felony. Mr. Mathews is scheduled to have a bail hearing in Maryland on Wednesday.

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“We can’t let Virginia go to waste, we just can’t,” the documents allege that Mr. Mathews said in late December.

The rally took place without incident on Monday, after the Governor of Virginia declared a state of emergency and banned weapons from the grounds of the legislature for five days.

U.S. police arrested several alleged members of violent white-supremacist groups – including Mr. Mathews and his two American co-accused – last week.

On Tuesday, prosecutors revealed more details of the alleged conspiracy in a 28-page memo outlining conversations they say took place in the apartment where Mr. Mathews lived with co-accused Brian Lemley, a former U.S. Army Cavalry Scout.

Open this photo in gallery A U.S. district court document image of Patrik Mathews, left, and Brian Lemley, leaving a store in Delaware after purchasing approximately 150 rounds of 5.56mm ammunition and paper shooting targets. AEly/Courtesy of manufacturer

Mr. Mathews, 27, disappeared from his home in Manitoba last August after media reports said he had ties to The Base, a violent white-supremacist group. Police say that members of this organization believe the United States is destined for a race war and want to accelerate it with acts of violence.

On Dec. 13, police infiltrated the apartment when no one was inside it. They discovered knives, assault-rifle components and military-style food rations, the prosecutors’ memo says.

Copied data from electronic devices revealed several propaganda videos – including ones featuring Mr. Mathews wearing a gas mask and ranting about race war, the memo states.

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“Your two options are as follows,” the document quotes him as saying in one such video. “Option No. 1, prepare for the collapse. Option number two, bring the collapse.”

In a conversation recorded on an FBI listening device planted in the apartment, Mr. Lemley talked about using a night-vision rifle scope to shoot at protesters and police at the rally, the memo says. “All you gotta do is start making things go wrong and [see] if Virginia can spiral out to … full-blown civil war,” Mr. Mathews allegedly replied.

Police say that during the first two weeks of January, the two men were seen stocking up on food and bullets and taking target practice at a range where they fired an assault rifle cobbled together from parts.

On Jan. 15, they also discussed their potential arrests. “You realize they’re just going to call us terrorists," Mr. Mathews said, according to the memo.

The two men put up a struggle the next day as they were arrested by an FBI-led joint terrorism task force. Both smashed their cellphones and dumped them into the toilet.

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