Protesters chained themselves to the doors of the police headquarters in Oakland, California, on Monday, prompting several arrests, and one demonstrator scaled a flagpole to hang a "Black Lives Matter" banner in front of the building.
Oakland and neighboring Berkeley have been the site of demonstrations for more than a week over decisions by grand juries not to charge white police officers in the killings of unarmed black men in Ferguson, Missouri and New York City.
Scores of people have been arrested as police in riot gear face off with protesters, some of whom have thrown rocks at the officers and looted businesses.
Most of the confrontations have happened after dark, but on Monday morning more than two dozen demonstrators used PVC tubes, ropes and locks to chain their arms together and block entrances to the Oakland Police Department.
Meanwhile, another group of protesters used similar tactics to chain themselves together to disrupt traffic at two nearby downtown intersections amid a heavy downpour.
At police headquarters, officers and firefighters used cutting tools to separate the demonstrators chained together at the doors, and several were taken into custody.
Officer Johnna Watson of the Oakland Police Department said 25 people were arrested for various offenses including blocking a public building, and obstructing or delaying a police officer.
The protester who climbed the flagpole stayed up there for several hours, Watson added, but eventually climbed down.
The protests in California's Bay Area have been among the most turbulent of a wave of demonstrations across the country over concerns about the policing of black communities.
On previous evenings last week, riot police fired tear gas and pepper spray to disperse crowds of demonstrators that were sometimes hundreds strong.
On Wednesday night, a Reuters photographer saw an undercover California Highway Patrol detective pull a gun on protesters after he and his partner were attacked.
Local activist Wazi Maret Davis said that by demonstrating in front of police headquarters they were sending a message that law enforcement is waging a conflict against blacks.
"The police system and the police are a huge part in leading the war against black people," Davis said. "That's why we bring our demands to their house."
