Police have shut down a counter-protest at a public square in downtown Portland, Oregon, because they say demonstrators were hurling bricks and other objects at officers.

Portland police cleared people out of Chapman Square near where a free speech rally was being held Sunday afternoon. Officers are using “less-lethal chemical munition” such as tear gas to disperse the crowds.

Police said people gathered at the free speech rally organized by the conservative group Patriot Prayer and other counter-protesters at City Hall were not involved.

At least three people have been arrested in a day of protests that drew thousands to the blocks around City Hall with competing messages.

The events follow the fatal stabbing of two Portland men who tried to stop another man’s anti-Muslim tirade.