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, Calif.
Riot police arrested dozens of protesters in the city's downtown, where bands of demonstrators threw chunks of concrete and metal pipes as well as lit roman candles and firebombs, police said. At least four protesters and several officers were injured.
"I think it will allow detractors to criticize the movement," protester Hale Nicholson said.
The protest outside the Port of Oakland, which reopened Thursday, represented an escalation in tactics as 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, so far mostly isolated in a city with a history of tensions between residents and police, will galvanize protesters or hurt their cause.
Nicholson blamed the violence on a small group of young people just there for violence - "Some kids looking to blow off some steam."
In Los Angeles, a spokesman for the encampment there, said those demonstrators don't represent the movement.
"We are about peace. That's the most powerful tool we have," said Mario Jefferson of the Occupy LA encampment, noting that the movement attracts many types of people, including some prone to violence.
"We don't want to waste energy on breaking things. We're trying to do this thing peacefully," he said.
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 they 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 viewed the strike and port shutdown as a significant victory.
Police, who had little to no 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.
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 port sends goods primarily to Asia, including wine as well as rice, fruits and nuts, and handles imported electronics, apparel and manufacturing equipment, mostly from Asia, as well as cars and parts from Toyota, Honda, Nissan and Hyundai.
An accounting of the financial toll from the shutdown was not immediately available.
His comments came before a group of protesters broke into the former Travelers Aid building in order to, as some shouting protesters put it, "reclaim the building for the people."
The potential for the chaos that ultimately erupted was not something Riley wanted to even consider.
"If they do that after all this ..." he said, pausing cautiously, then adding, "They're smarter than that."
Occupy protesters voicing anger over a budget trim that forced the closure of a homeless aid program converged on the empty building where it had been housed just outside of downtown.
They blocked off a street with wood, metal Dumpsters and other large trash bins, sparking bonfires that leapt as high as 15 feet in the air.
City officials later released a statement describing the spasm of unrest.
"Oakland Police responded to a late night call that protesters had broken into and occupied a downtown building and set several simultaneous fires," the statement read. "The protesters began hurling rocks, explosives, bottles, and flaming objects at responding officers."
Several businesses were heavily vandalized. Dozens of protesters wielding shields were surrounded and arrested.
Protesters ran from several rounds of tear gas and bright flashes and deafening pops that some thought were caused by "flash bang" grenades. Fire crews arrived and suppressed the protesters' flames.
Protesters and police faced off in an uneasy standoff until the wee hours of the morning.
It is the kind of posture that Oakland is familiar with. It was the scene of violent protests in 2009 and 2010 over the killing of an unarmed black man by a white transit officer. Downtown businesses were looted, windows smashed and fires set.
Then, as now, police blamed the violence on a small group of anarchists, many from outside the city.
In 2003, a police crackdown on an anti-war demonstration at the Port of Oakland left protesters and dockworkers hospitalized and resulted in police getting a new, stricter crowd-control policy.
The history of clashes goes back even further to demonstrations in the 1960s over the Vietnam War and the draft, among other issues.
For most of Wednesday, peace prevailed at the rallies in Oakland, even attracting families, some taking their children along in strollers. Protesters hung a large black banner downtown that read: "DEATH TO CAPITALISM."
During the rally, some protesters broke away and picketed outside nearby banks. Some of the buildings were vandalized.
Further away from the rally, vandals shattered a Chase bank branch and splattered ink all over an ATM. Someone later taped a note to the shattered glass that read: "We are better than this. ... Sorry, the 99 percent."
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 kids 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."
Associated Press writers Garance Burke, Marcus Wohlsen and Beth Duff-Brown in San Francisco, Terry Collins and Terence Chea in Oakland, Calif., Mark Pratt in Boston, JoAnn Loviglio in Philadelphia, Jon Fahey and Verena Dobnik in New York and Christina Hoag in Los Angeles contributed to this report.