Salt Lake City, Utah - A shooting at a protest against President Donald Trump's policies in Utah left one person with "life-threatening injuries," police said, adding that three others were taken into custody.

Police said the incident occurred around 8:00 PM Saturday in Utah's capital Salt Lake City during a protest that drew about 10,000 people – one of several "No Kings" demonstrations across the US rallying against Trump.

"We can confirm the shooting resulted in one person being critically injured. The patient has been taken to a hospital with life-threatening (injuries)," said the Salt Lake City police department in a social media post, adding that they had "a person of interest in custody."

Police Chief Brian Redd stressed during a news conference that the events leading up to the shooting "were very peaceful," adding that the first person taken in custody had a gunshot wound and was transported to the hospital.

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Two other individuals involved in the incident were also taken into custody, he said.

"At this time, there is... no ongoing threats to the public," Redd said, adding that it was too early in their investigation to say if the shooting was politically motivated.

Mayor Erin Mendenhall said "this act of violence does not define" Salt Lake City – a Democratic bastion in the deep-red Utah.

"The purpose of today's demonstration was a powerful and peaceful expression until this event and that cannot be overshadowed or silenced by a single act meant to harm," she said.

"We are a nation that needs our First Amendment right, we deserve to protest in peace. And what happened today I hope will not silence the voices of the public who deserve to have their voices heard."

Salt Lake City Police Chief Brian Redd confirmed at a press conference that the victim in Saturday's shooting – identified as 39-year-old Arthur Folasa Ah Loo – had succumbed to his injuries.

"Our victim was not the intended target, but rather an innocent bystander participating in the demonstration," Redd said, per the Salt Lake Tribune.

He also clarified that two people initially detained after the incident had been released without charges, and that the main suspect, Arturo Gamboa, was cooperating with investigators.