The organizer of a right-wing rally scheduled to take place Sunday in Berkeley, Calif., has canceled the event and is urging others not to attend out of concern it could result in violent clashes with counter-protesters.

“I’m sorry for this but I want this event to happen peacefully and I do not want to risk anyone getting harmed,” organizer Amber Cummings wrote in a statement to the Los Angeles Times about the event, which was called “No to Marxism in America.”

She said she had concerns about the presence of counter-protesters from anti-fascist groups, often known as “antifa,” that have drawn attention for sometimes employing militant tactics. Antifa protesters, who have also been the targets of violence, caused more than $100,000 in property damage at the University of California, Berkeley earlier this year in opposition to a speech by far-right speaker Milo Yiannopoulos.

“I will attend this event alone and I stress please stop the violence,” Cummings said.

Another right-wing event scheduled to take place in San Francisco on Saturday was canceled and turned into a news conference, the Los Angeles Times reported.

“We have a lot of respect for the citizens in San Francisco and at the end of the day, we want people to be safe,” Joey Gibson, founder of the Patriot Prayer group and organizer of the Freedom Rally event, told the Times. “In our opinion, it seems like it would have been a huge riot.”

Organizers of both events said they were not affiliated with racist or white supremacist groups but worried the rallies might be co-opted by such groups. Similar concerns about the presence of white supremacists at a right-wing “Free Speech” rally in Boston last week drove an estimated 40,000 people to march in protest of the event.

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Write to Katie Reilly at Katie.Reilly@time.com.