(Reuters) - Police in Portland, Oregon arrested at least 13 people on Saturday as a right-wing group marched to a downtown waterfront park and anti-fascist counterprotesters scuffled with officers who tried to keep the two sides apart.

A rally by hundreds of supporters of the right-wing Proud Boys organization was met by a similar number of “antifa” opponents, and isolated clashes broke out between both sides and between antifa and police as the gathering wrapped up.

At least six people suffered minor injuries, according to police. One person was taken to a hospital. Officers said they seized weapons including chemical sprays, shields, metal and wooden poles, knives, and a stun gun from multiple groups.

At the peak of the demonstrations there were an estimated 1,200 protesters on the streets of the downtown district, said Portland Police Chief Danielle Outlaw.

Charges against those in custody would include disorderly conduct, interfering with police, resisting arrest, and unlawful use of a weapon, she said at a news conference.

Right-wing and anti-fascist factions have clashed in Portland several times in recent months, including a rally that turned violent in July last year.

Hours ahead of Saturday’s competing demonstrations, U.S. President Donald Trump said “major consideration” was being given to designating antifa as a terrorist organization.

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“Portland is being watched very closely. Hopefully the Mayor will be able to properly do his job!” Trump wrote on Twitter.

Ted Wheeler, Portland’s mayor, said he was not concerning himself with tweets from Washington, and he praised the response by law enforcement.

“I’m grateful that this was largely a peaceful event,” Wheeler told reporters at the news conference.

“Police did an exemplary job of de-escalating the situation, keeping the extremists on both sides separated for the most part, and preventing people who wanted to engage in acts of violence from confronting each other.”