OAKLAND, CALIF. — Occupy Wall Street supporters who staged rallies that shut down the nation's fifth-busiest port during a day of protests condemned on Thursday the demonstrators who clashed with police in the latest flare-up of violence in Oakland.
Riot police arrested more than 80 protesters in the city's downtown, where bands of demonstrators threw chunks of concrete and metal pipes and lit roman candles and firebombs, police said. Five protesters and several officers were injured.
"I think it will allow detractors to criticize the movement," said protester Hale Nicholson. He has been staying at the Occupy Oakland encampment and said he and most people there are pacifists.
The protest outside the Port of Oakland, which reopened Thursday, represented an escalation in tactics when a movement that had largely been about marches, rallies and tent camps targeted a major symbol of the nation's commerce.
The violence that followed, however, raised questions about the direction of the movement and whether the clashes, thus far mostly isolated in a city with a history of tensions between residents and police, will galvanize protesters or hurt their cause.
The clashes provide fresh ammunition to critics of the Occupy movement, who say the anti-capitalist protests promote class division and lack clear goals and logistical controls.
Mr. Nicholson blamed the violence on a small group of young people just there for violence "Some kids looking to blow off some steam."
The far-flung movement challenging the world's economic systems and distribution of wealth has gained momentum in recent weeks, capturing the world's attention as supporters set up tent camps from New York's Wall Street to Los Angeles' Skid Row.
Oakland became a rallying point last week after an Iraq war veteran was injured when protesters and riot police battled in the streets.
Organizers called for a general strike on Wednesday, and supporters in New York, Philadelphia, Los Angeles and elsewhere staged smaller-scale demonstrations, some in solidarity with their Oakland counterparts.
Oakland protesters said they viewed the strike and port shutdown as a significant victory.
Police, who had little presence during the protest during the day, said that about 7,000 people participated in demonstrations that were peaceful except for a few incidents of vandalism at local banks and businesses.
"We put together an ideological principle that the mainstream media wouldn't talk about two months ago," organizer Boots Riley said.
Mr. Riley, whose anti-capitalist views are well documented, considered the port shutdown particularly significant for organizers who targeted it in an effort to stop the "flow of capital."
The clashes in Oakland came as the Occupy movement continued its activities in cities across the country.
In Philadelphia, protesters were arrested as they held a sit-in at the headquarters of cable giant Comcast. In New York, about 100 military veterans marched in uniform and stopped in front of the New York Stock Exchange, standing in loose formation.
The veterans were also angry that returned from war to find few job prospects.
In Boston, college students and union workers marched on Bank of America offices, the Harvard Club and the Statehouse to protest the nation's burgeoning student debt crisis.
And among the other protests in Oakland, parents and their children joined in by forming a "children's brigade."
"There's absolutely something wrong with the system," said Jessica Medina, a single mother who attends school part time and works at an Oakland cafe. "We need to change that."