OAKLAND, Calif. - For weeks the protests had waned, with only a smattering of people taking to Oakland's streets for occasional weekend marches that bore little resemblance to the headline-grabbing Occupy demonstrations of last fall.
Then came Saturday, which started peacefully enough - a midday rally at City Hall and a march. But hours later, the scene near downtown Oakland had dramatically deteriorated: clashes punctuated by rock and bottle throwing by protesters, volleys of tear gas from police, and a City Hall break-in that left glass cases smashed, graffiti spray-painted on walls and an American flag burned.
More than 400 people were arrested on charges ranging from failure to disperse to vandalism, police spokesman Sgt. Jeff Thomason said. At least three officers and one protester were injured.
On Sunday, city officials vowed to be ready if Occupy protesters try to mount another large-scale demonstration. Protesters decried Saturday's police actions as illegal and threatened to sue.
Mayor Jean Quan inspected damage caused by dozens of people who broke into City Hall. She said she wants a court order to keep Occupy protesters who have been arrested several times out of Oakland, which has been hit repeatedly by demonstrations that have cost the financially troubled city about $5 million.
Quan also called on the loosely organized movement to "stop using Oakland as its playground."
Saturday's protests were the most turbulent since police forcefully dismantled an Occupy encampment in November.
After the mass arrests, the Occupy Oakland Media Committee criticized the police's conduct, saying that most of the arrests were made illegally because police failed to allow protesters to disperse. It threatened legal action.
"Contrary to their own policy, the OPD gave no option of leaving or instruction on how to depart. These arrests are completely illegal, and this will probably result in another class action lawsuit against the OPD," a release from the group said.
Deputy Chief Jeff Israel told reporters late Saturday that protesters gathered unlawfully and police gave them multiple verbal warnings to disband.