Thousands of counter-protesters marched through downtown Boston on Saturday to condemn neo-Nazis and white nationalism as conservative and libertarian activists mounted a "Free Speech Rally" at Boston Common in the aftermath of deadly clashes last week in Virginia.

Boston police said at least 15,000 counter-protesters were peacefully marching toward the park where the rally was being held in a large area encircled by metal barriers.

Many carried signs saying "Love your neighbor,” “Resist fascism” and “Hate never made U.S. great.” Others carried a banner reading: “SMASH WHITE SUPREMACY.”

City officials made no secret of their wish that marchers on all sides would have stayed away, given the level of violence that erupted in Charlottesville, where a counter-protester were killed.

"If anyone gets out of control — at all — it will be shut down,” said .Mayor Marty Walsh.

Police Commissioner William Evans said 500 officers — some in uniform, others undercover — were deployed to keep the two groups apart during the two-hour rally.

Boston placed tight restrictions on rallygoers, banning backpacks, sticks or anything that wcould be turned into a weapon.

“We will not tolerate any misbehavior, violence or vandalism whatsoever,” Evans said.

Boston Free Speech Coalition, which organized the two-hour rally, said on Facebook that it is not affiliated with the Charlottesville rally organizers in any way. “We are not associated with any alt-right or white supremacist groups,” the coalition said. “We are strictly about free speech.”

The coalition said on its Facebook page that speakers will include Joe Biggs, who recently worked for AlexJones' conspiracy friendly website Infowars, and Kyle Chapman, also known as "Based Stickman,” and who founded the Fraternal Order of Alt-Knights, which the Southern Poverty Law Center calls a “new Alt-Right group of street fighters.”

Opponents feared that white nationalists might show up in Boston anyway, raising the specter of ugly confrontations in the first potentially large and racially charged gathering in a major U.S. city since Charlottesville.

Events also were planned Saturday for Atlanta and Dallas.

For their part, counter-protesters from Black Lives Matter and other groups condemning racism and anti-Semitism planned to march from the city’s Roxbury neighborhood to the Common while a second group planned to rally on the steps of the Statehouse overlooking the park.

Photos: Thousands march in Boston for protests a week after deadly demonstration

The 383-year-old Boston Common — the nation’s oldest city park — has been the site of numerous rallies and protests for centuries.

Monica Cannon, an organizer of the "Fight White Supremacy" march, tells Reuters that "(i)gnoring a problem has never solved it."

"We cannot continue to ignore racism, ignore white supremacism, ignore neo-Nazis and pretend it's not a problem," she said.

The Charlottesville clashes, that left one counter-protester dead, erupted after white nationalists, white supremacists, KKK supporters and neo-nazis tried to hold an officially permitted "Unite the Right" rally at a downtown park to protest the city's decision to remove a statue of Robert E. Lee in the center of the Virginia college town.

The rally was declared an "unlawful assembly" by the city only minutes before it was scheduled to begin after street brawls erupted between protesters and counter-protesters.

Contributing: Associated Press