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(CNN) -- Authorities made a series of arrests at Occupy Wall Street protests in California and Georgia on Tuesday and Wednesday, with clashes in one city that involved tear gas being used on demonstrators.
Police said they fired the tear gas on protesters in Oakland, California, after the crowd threw paint and other objects at officers.
Among the injured in the clash was a two-time Iraq war veteran, Scott Olsen, who sustained a skull fracture after allegedly being shot in the head with a police projectile, according to Iraq Veterans Against the War.
Olsen, a former Marine, was in serious but stable condition Wednesday afternoon at Highland General Hospital in Oakland, said Dottie Guy, a member of the veterans group who told CNN by phone that she was visiting Olsen at the hospital.
Among a growing number of war vets participating in the Occupy movement, Olsen was peacefully marching from a downtown library toward City Hall in an effort to reclaim an encampment that had been cleared out by police, the veterans group said.
During Tuesday's clash in Oakland, plumes of smoke could be seen in the city as about 500 people defied calls to leave an area of downtown Oakland, according to police. Protesters had camped for weeks in several areas in the city, including near City Hall, police said.
"The city remains committed to respecting free speech as well as maintaining the city's responsibility to protect public health and safety," Oakland police said in a statement.
Oakland resident Andrew Johnson said he decided to leave when police threatened arrests, soon after hearing explosions as tear gas canisters were fired into the air.
"I think at first it was a pretty inspiring sight," he said of the protesters. "It was inspiring to see people so impassioned. But when the police action began, it was a pretty unnerving sight. Just to see that energy turn into panic and anger was unsettling."
In Atlanta, police arrested demonstrators at a downtown park overnight. The arrests came after Atlanta Mayor Kasim Reed said he sent ministers to the park "to see if we can find a way to resolve this amicably."
Reed told CNN affiliate WSB that concerns were increased when a man in the park was seen with an assault rifle. "We could not determine whether the weapon was loaded and could not get additional information on the weapon," he said.
Authorities ordered people to leave the park around midnight Tuesday, WSB said, going from tent to tent with flashlights. Arrests began taking place about 12:45 a.m.
Organizers had asked protesters to be peaceful if police took action, and most were, WSB said. Many gathered in the center of the park, locked arms and sang "We Shall Overcome," as police led them one by one to waiting buses.
A protester at the park said he was scared. "It's very intimidating," said Malcolm McKenzie. "I believe what we're doing is right, but we're going to jail. It hurts to see America do this to people who want change."
It was unclear how many people were arrested in the two cities. CNN affiliate KGO reported that at least 85 people were arrested during an early morning raid in one part of Oakland and there were other arrests throughout the day. In Atlanta, WSB reported 53 were arrested.
In Oakland early Tuesday, police dismantled a tent camp set up by protesters in a city park.
The overnight camping had to end because of health and safety concerns, Oakland police said in a statement.
"There were a series of safety conditions, including numerous reports of fighting, assault and threatening/intimidating behavior" at the camp, police said in a statement. Medical responders could not get to the scene to provide medical care on at least two occasions, and fire and police also could not get through.
"Sanitation conditions worsened with frequent instances of public urination and defecation, as well as improper food storage," the police statement said. "The existing rodent problem in the park was exacerbated, and authorities were unable to control it because of the campers' presence. Graffiti, litter and vandalism also posed problems, police said.
After the camp was dispersed, the protesters reconvened for demonstrations later in the day, the affiliates said, prompting the new clashes.
Video from the Oakland clashes showed a chaotic scene, with protesters running from clouds of tear gas.
Oakland and Atlanta are two of many cities worldwide dealing with the Occupy Wall Street protests, the leaderless movement that started in New York in September.
Demonstrators have typically railed against what they describe as corporate greed, arrogance and power, as well as repeatedly stated their assertion that the nation's wealthiest 1% hold inordinate sway over the remaining 99% of the population.
Meanwhile, Occupy Wall Street expanded its message to include a call for better health care for the "99 percent," marching to a shuttered Greenwich Village hospital slated to become high-end condominiums.
Several hundred protesters from Zuccotti Park spent their afternoon connecting their message to the health care debate, converging on the offices of Blue Cross Blue Shield, rallying with doctors and nurses, before heading to the site of the former St. Vincent's Hospital.
The hospital closed April 30, 2010, and there has been a bitter public debate since over plans to build high-end condominium apartments in a neighborhood with overcrowded schools and no other public health care.
CNN's Michael Martinez, Amber Lyon, Steve Turnham, Rose Arce, Nick Valencia, Jessica Jordan and Rich Phillips contributed to this report