Police clad in riot gear and armed with tear gas cleared out Oakland's anti-Wall Street encampment early Monday, the latest law enforcement crackdown amid complaints around the country of health and safety hazards at protest camps.

The raid at the Occupy Oakland camp, one of the largest and most active sites in the movement, came a day after police in Portland, Ore., arrested more than 50 people while shutting down its camp amid complaints of drug use and sanitation issues.

Police in Burlington, Vt., also evicted protesters after a man fatally shot himself last week inside a tent.

Police staged a previous raid on the Oakland encampment Oct. 25, but Mayor Jean Quan allowed protesters to re-establish their tent city. On Monday, however, Quan said officials could no longer ignore the problems the camp posed.

"We came to this point because Occupy Oakland, I think, began to take a different path than the original movement," Quan said. "The encampment became a place where we had repeated violence and last week a murder. We had to bring the camp to an end before more people got hurt."

Demands increased for Oakland protesters to pack up after a man was shot and killed Thursday near the encampment at the City Hall plaza.

Protesters claimed there was no connection between the shooting and the camp. But police identified the slain man as Kayode Ola Foster, 25, of Oakland, saying his family confirmed he had been staying at the plaza.

Witnesses also told police that one of two suspects in the shooting had also been a frequent resident at the plaza. The names of the suspects have not been released.

Monday's raid came as no surprise to protesters after the city issued its fourth order to abandon the camp. About 300 officers from theOakland Police Department and seven other law enforcement agencies moved in around 5:30 a.m., arresting 33 people and tearing down about 150 tents.

Another man was arrested later in the morning for trying to break through police barricades and spitting on officers.

Protesters vowed to regroup and return.

"I don't see how they're going to disperse us," said Ohad Meyer, 30, of Oakland. "There are thousands of people who are going to come back."

Officials declared the operation a success, saying all arrests were peaceful and there were no reported injuries to protesters or officers. Police said those taken into custody likely will face charges of unlawful assembly and lodging.

"This had been a very difficult situation," Quan said. "I'd tried to do what was right for the city and keep the most people safe at every step."

Not everyone in Quan's camp agreed with the show of force.

Dan Siegel, one of the mayor's top legal advisers, resigned over Monday's raid, saying officials should have done more to work with protesters before sending in police. Siegel, a longtime friend of Quan who worked as an unpaid adviser, has been a vocal critic of Oakland police and their handling of the Oct. 25 raid.

Video footage of a protest after the Oct. 25 raid showed officers using flash-bang grenades and firing beanbag rounds into the crowd, injuring a number of people and prompting cries of police brutality.

Marine Corps veteran Scott Olsen was left in critical condition after suffering a head injury during that protest. His case became a rallying cry for the Occupy Wall Street movement around the nation.

Olsen, 24, issued his first statement Sunday since leaving a hospital.

"You'll be hearing more from me in the near future and soon enough we'll see you in our streets!" he posted on his Google+ account with a photograph of himself with a neck brace and apparent bruising around his left eye.

Protesters in Portland had been ordered to leave their encampment by midnight Saturday. However, in the hours leading to the deadline, thousands of protesters flooded two blocks of parkland where an Occupy encampment first appeared Oct. 6.

Riot police moved into the Portland camp shortly after noon Sunday, using a loudspeaker to warn that anyone who resisted risked arrest and "may also be subject to chemical agents and impact weapons." Demonstrators chanted "we are a peaceful protest."

Officers used batons to shove a cluster of protesters out of the camp and dragged out those who resisted, including some who were holed up in a makeshift fort made of plywood, pallets, shopping carts and other debris.

A total of 51 protesters were arrested during the Sunday afternoon action.

One man was taken away on a stretcher. He was alert and talking to paramedics and raised a peace sign to fellow protesters, who responded with cheers.

Portland Mayor Sam Adams defended his order to clear the parkland, saying it is his job to enforce the law and keep the peace. Police finished cleaning up the area Monday, and officials reported no major disturbances.

In Vermont, protesters agreed to remove their tents from a Burlington park Sunday in a resolution Police Chief Michael Schirling described as "amicable."

Police and city officials initially agreed to let the protesters stay in the park after a 24-hour protest began but changed their minds after Joshua Pfenning shot himself. Authorities said the tents had to be removed because police could not see what was going on inside.

Officials in Oakland, Burlington and other cities said protesters would be allowed to gather again at the site of their former camps as long as they didn't spend the night.

Oakland Police Chief Howard Jordan said a strong police presence would remain at the plaza around the clock to make sure protesters didn't roll out tents and sleeping bags again.

The city said Monday that it's spent an estimated $2.4 million on efforts to contain the protest movement in the last month.

Late Monday afternoon, a few hundred people regrouped at the city's main library and marched to the cleared and cleaned plaza. The police chief said they would be allowed to assemble as long as they remained peaceful and did not try to re-establish the encampment.

Shon Kae, who's on the Occupy Oakland media committee, said it was still unclear what demonstrators' next move would be.

"There is no secret plan," Kae said. "We all have to just keep on with the struggle."