A Tennessee man is facing federal charges after allegedly brandishing a firearm at protesters earlier this month, with prosecutors expressing concerns about his “desire to commit an act of mass violence,” according to court documents.

Elijah Millar, 19, of Murfreesboro, Tennessee, was charged Friday with unlawful possession of a firearm, the Justice Department announced. He faces up to 15 years in federal prison and a maximum fine of $250,000 if convicted.

According to prosecutors, Millar, dressed in all-black clothing and wearing a mask, confronted demonstrators at a “No Kings” protest near Nashville’s Bicentennial Mall on June 14.

Witnesses reported that Millar spat at protesters, yelled at them, and brandished a Sig Sauer 9mm pistol before being apprehended by Metropolitan Nashville Police Department officers, the DOJ said.

Just three days after being released on bond, Millar was arrested again when Murfreesboro Police Department officers discovered another loaded 9mm firearm in his waistband, authorities said.

Court documents said Millar was previously subject to a 2023 emergency conservatorship order in Rutherford County, Tennessee, which prohibited him from possessing firearms after finding he was “at risk of substantial harm to his health, safety, and welfare.”

A subsequent order in September 2024 designated him as a “disabled person needing care” and further restricted his access to firearms.

“The right to peaceably protest government action is guaranteed by the First Amendment and cannot be infringed upon by armed individuals whose actions put people in danger,” said Acting United States Attorney Robert E. McGuire.

On Sunday, prosecutors urged the court to keep Millar in custody, citing social media posts and online activity that suggested “a desire to commit an act of mass violence.”

The incident comes amid heightened tensions at “No Kings” protests nationwide. In a separate incident on the same day in Utah, a protest turned deadly when a safety volunteer accidentally shot and killed a demonstrator while responding to another armed individual who allegedly approached the crowd with a rifle.

The case is being investigated by the FBI’s Nashville Field Office, the Metropolitan Nashville Police Department, and the Murfreesboro Police Department.

ABC News’ Alexander Mallin contributed to this report.