An Antifa protest in Berkeley became violent on Sunday when members of the group smashed the windows of a Marine Corps recruiting office. A series of photos posted on Twitter show Antifa members, self-styled anti-facists who use violence to oppose those they identify as fascists, racists or right wing extremists, destroying the windows of the Shattuck Avenue office.

Twenty people were arrested during competing demonstrations by Antifa and individuals connected to the alt-right. Three people were hurt after authorities say “extremists” threw explosives at police officers, Fox News reports. The explosives are believed to have consisted of fireworks and flares.

Video posted on Twitter shows individuals dressed in black using hammers to smash windows at the Marine Corps office.