A right-wing group and counter-protesters are staging opposing rallies in Portland, Oregon, as police try to prevent the gatherings from turning violent.
A rally organised by Patriot Prayer leader Joey Gibson is the third to take place in the city in Oregon state this summer.
Two previous events ended in fighting and riots, and one counter-protester was sent to hospital with a skull fracture.
This time, Mr Gibson changed the venue from a federal plaza outside the US district court to a waterfront park, so that some of his Oregon supporters can carry concealed weapons as they demonstrate.
Chartered buses have brought participants from Vancouver, Washington – where Mr Gibson lives – to Portland with armed security on board.
Protesters saw a significant police presence, including bomb-sniffing dogs and weapons-screening checkpoints.
Mr Gibson’s insistence on bringing his right-wing supporters repeatedly to this Democrat-supporting city has crystallised a debate about the limits of free speech in an era of stark political division.
Patriot Prayer has held rallies in many other cities around the western US, including Berkeley, California, which have drawn violent reactions.
The Portland events have taken on a larger significance after a Patriot Prayer sympathiser was charged with fatally stabbing two men who came to the defence of two young black women – one in a hijab – whom the attacker was accused of harassing on a light-rail train in May 2017.
A coalition of community organisations and a group representing more than 50 tribes warned of the potential for even greater violence than previous rallies if participants carry guns.
It called on officials to denounce what it called “the racist and sexist violence of Patriot Prayer and Proud Boys” and protect the city.
Portland police said weapons may be seized if there is a violation of law, and added that it is illegal in Portland to carry a loaded firearm in public unless a person has a valid Oregon concealed handgun licence.
Many protesters are expected to come from out of state.
Mr Gibson, who is running a long-shot campaign to unseat Democratic US senator Maria Cantwell in Washington state, said earlier this week that he will not stop bringing his followers to Portland until they can express their right-wing views without interference.
He said: “I refuse to do what Portland wants me to do because what Portland wants me to do is to shut up and never show up again.
“So yeah, I refuse to do that, but I will not stop going in, and I will not stop pushing, and I will not stop marching until the people of Portland realise that and realise that their methods do not work,” he said.
Self-described anti-fascists – or “antifa” – have been organising anonymously online to confront Patriot Prayer and an affiliated group, the Proud Boys, in the streets.
A broader counter-protest organised by a coalition of unions, immigrant rights groups and artists will gather at City Hall before the Patriot Prayer rally.
Organisers said that while Patriot Prayer denies being a white supremacist group, it affiliates itself with known white supremacists, white nationalists and neo-Nazi gangs.
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