OAKLAND, Calif. (AP) -- Anti-Wall Street demonstrators held vigils for an Iraq War veteran seriously injured during a protest clash with police in California as some Occupy encampments came under growing pressure from authorities to abandon sites in parks and plazas.

A crowd of at least 1,000 people, many holding candles, gathered Thursday night in Oakland in honor of 24-year-old Scott Olsen, who is hospitalized with a fractured skull.

Many in the crowd shooed away Oakland Mayor Jean Quan who retreated back into City Hall after trying to address them during a tense late-night appearance. She apologized to Olsen during a hospital visit earlier Thursday.

"I am deeply saddened about the outcome on Tuesday. It was not what anyone hoped for, ultimately it was my responsibility, and I apologize for what happened," Quan said in a written statement to protesters late Thursday. "I cannot change the past, but I want to work with you to ensure that this remains peaceful moving forward."

In Nashville, police cracked down overnight on an Occupy protest camp near the Capitol under a new policy setting a curfew for the complex. Officers moved in a little after 3 a.m. and arrested about 30, who were later released after a judge wouldn't sign the warrants. About 20 protesters who stayed on a nearby sidewalk were not arrested and were still there later in the morning as state troopers stood guard at the steps to the Capitol.

Protesters also held a vigil for Olsen in Las Vegas, which drew a handful of police officers. Afterward, protesters invited them back for a potluck dinner.

"We renewed our vow of nonviolence," organizer Sebring Frehner said.

The Marine veteran, who won medals in Iraq, has become a rallying cry for the Occupy Wall Street demonstrators across the nation, with Twitter users and protest websites declaring, "We are all Scott Olsen."

Joshua Shepherd, 27, a Navy veteran who was standing nearby when Olsen got struck, called it a cruel irony that Olsen is fighting an injury in the country that he fought to protect.

Despite the financial underpinnings of the protests, Olsen himself wasn't taking part out of economic need.

His friends say he makes a good living as a network engineer and has a nice apartment overlooking San Francisco Bay. Still, he felt so strongly about economic inequality in the United States that he fought for overseas that he slept at a protest camp after work.

"He felt you shouldn't wait until something is affecting you to get out and do something about it," said friend and roommate Keith Shannon, who served with Olsen in Iraq.

It was that feeling that drew him to Oakland on Tuesday night, when the clashes broke out and Olsen's skull was fractured. Fellow veterans said Olsen was struck in the head by a projectile fired by police, although the exact object and who might have been responsible for the injury have not been definitively established. Officials are investigating exactly where the projectile came from.

Even as the vigil was held in Oakland, protest organizers prepared to defy Oakland's prohibition on overnight camping on the now patchy, manure-smelling lawn outside City Hall.

Shake Anderson, an organizer with Occupy Oakland, said half a dozen tents were erected on the plaza by midday Thursday where police armed with tear gas and bean bag rounds disbanded a 15-day-old encampment Tuesday. More than two-dozen tents had been erected as food and supplies arrived late Thursday.

"We believe in what we're doing," Anderson said. "No one is afraid. If anything, we're going to show there's strength in numbers."

Few police were seen in the area during late Thursday, as Quan in her written statement said that she and interim police chief Howard Jordan hope to meet with protesters and urged them again not to camp at the plaza.

Elsewhere across the United States, protesters brushed off pressure from authorities and maintained the camps that have sprung up in opposition to growing economic inequality.

Protesters at San Francisco's Justin Herman Plaza braced for a police raid early Thursday that never came. Still, police have warned the protesters that they could be arrested on a variety of sanitation or illegal camping violations.

Officials told protesters in Providence, R.I., that they were violating multiple city laws by camping overnight at a park.

Anti-Wall Street protesters camped out in downtown Los Angeles said they're planning to continue their demonstration indefinitely, although both they and the mayor's office were eyeing alternate sites.

Meanwhile, Olsen has been improving. Doctors transferred him from the emergency room to an intensive care unit and upgrading his condition to fair on Thursday.

Dr. Alden Harken, chief surgeon at Highland Hospital, said Olsen was still unable to speak but had improved dramatically since he was hospitalized unconscious with a fractured skull and bruised brain that caused seizures.

Harken said Olsen was interacting with his parents, who flew in from Wisconsin, doing math equations and otherwise showing signs of "high-level cognitive functioning." The doctor said he may require surgery, but that's unlikely.

"He's got a relatively small area of injury and he's got his youth going for him. So both of those are very favorable," Harken said.

Olsen smiled during Quan's visit and expressed surprise at all the attention his injury has generated, hospital spokesman Vintage Foster said.

His uncle in Wisconsin told The Associated Press that Olsen's mother was trying to understand what had happened.

"This is obviously a heartbreaker to her," George Nygaard said. "I don't think she understands why he was doing this."

The group Iraq Veterans Against the War blamed police for Olsen's injury. Jordan said the next day that Oakland police will investigate whether officers used excessive force.

Police have said they responded with tear gas and bean bag rounds only when protesters began throwing bottles and other items at them.

On Tuesday, Olsen had planned to be at the San Francisco protest, but he changed course after his veterans' group decided to support protesters in Oakland after police cleared a two-week long encampment outside City Hall.

"I think it was a last-minute thing," Shannon said.

A video posted on YouTube showed Olsen being carried by other protesters through the tear gas, his face bloodied. People shout at him: "What's your name? What's your name?" Olsen just stares back.

People at OPSWAT, the San Francisco security software company where Olsen works, were devastated after learning of his injuries. They described him as a humble, quiet man.

Olsen had been helping to develop security applications for U.S. defense agencies, building on expertise gained while on active duty in Iraq, said Jeff Garon, the company's director of marketing.

Olsen was awarded seven medals while serving in the U.S. Marine Corps, which he left as a lance corporal in November 2009 after serving for four years. One of them was the Navy-Marine Corps Achievement Medal.

Olsen moved to the Bay Area in July, and quickly found friends in the veterans against the war group.

His tours of duty in Iraq made him more serious, Shannon said.

"He wasn't active in politics before he went in the military, but he became active once he was out ... the experience in the military definitely shaped him," Shannon said.

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Dearen reported from San Francisco. Associated Press writers Dinesh Ramde in Milwaukee, Garance Burke in San Francisco, Julie Watson in San Diego, Lucas L. Johnson II in Nasvhille, Tenn., and Michelle Rindels in Las Vegas contributed to this report.

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