At least three people have been stabbed in a brawl between Ku Klux Klan (KKK) members and counter-protesters in Anaheim, California, US police said.
Thirteen people, both KKK members and rival demonstrators, were arrested.
The violence broke out when several Klan members arrived at a local park for a rally and were attacked by counter-protesters, according to police.
One of the stabbing victims is said to be in a serious condition.
A Klansman who allegedly stabbed one of the demonstrators with a flag pole is among those detained.
The flag pole, topped by an American eagle ornament, is believed to have been used to wound three demonstrators.
The counter-protests had been underway for hours before around six KKK members arrived, witnesses reported.
The Klan members held signs that read "White Lives Do Matter" and carried Confederate flags.
As the Klansmen unpacked the signs they were said to have been surrounded by demonstrators with wooden planks.
Some were seen kicking a man whose shirt read "Grand Dragon", the name of a high-ranking KKK member, reports said.
"These Klan guys were fighting for their lives" witness Darren Simpson told Reuters.
"A lot of us were trying to break it up," witness Dion Garcia, told Reuters.
"This was not necessary, they should've just let the Klan protest. This is America, we have free speech."
Another witness, Brian Levin, said after helping a Klansman away from the crowd, he asked him: "How does it feel that your life was just saved by a Jewish man?"
"Thank you," the man replied, according to Mr Levin.
"All hell broke loose" Mr Levin said. "I thought they were going to stomp these Klansmen to death".
The Ku Klux Klan is one of the oldest and most infamous hate groups in the US, and has targeted African Americans, Jews, Catholics and immigrants, according to the Southern Poverty Law Center, which tracks hate groups.
The group has a long history in Anaheim, with KKK members elected to the city council in the 1920s.