A man was shot and killed in Oakland's Frank Ogawa Plaza on Thursday evening, just yards from the entrance to the Occupy Oakland encampment.

The killing, which came as hundreds of occupiers prepared to celebrate the camp's one-month anniversary, prompted Oakland Mayor Jean Quan to call for the campers "to leave voluntarily tonight."

The man, who was shot in the head, was not immediately identified.

The violence occurred on the same day as UC Berkeley police defended their crackdown on Occupy Cal.

Oakland City Council president Larry Reid condemned the shooting and said it was yet more proof that the tent city needed to be dismantled. "We can no longer continue to sit back," he said. "This has raised the red flag even more."

According to witness accounts, a small fight broke out in the camp between two young men.

"I heard gunshots, and everybody started running," said Kevin Jenkins, 24, an Oakland native who witnessed the shooting.

After the initial fight, one of the young men called several friends or family members from outside the camp and asked them to come and help him. The victim had visited the camp often, said his cousin, Medea Williams of Oakland, who said she lived in a camp tent.

When the friends arrived, the dispute escalated into pushing and shoving near the portable toilets adjacent to the plaza.

According to one witness and Occupy Oakland supporter, Rachel Tolmachoff, 55, of Pleasant Hill, a group of occupiers then intervened and tried to get the people involved in the fight to move on. A short time later, they heard between four and six gun shots and saw several men run by.

One of the men involved may have run down to the BART station on 14th and Broadway.

Mike Tarmo, 31, a native of Sierra Leone, said he also saw the shooting. Tarmo claimed that the group of outsiders simply walked up to a man standing on the steps of the plaza and started beating and punching him. The occupiers tried to step in, Tarmo said. "There were 20 Occupy guys going to help him, saying, Stop! Stop!" Tarmo said the victim of that physical assault was the same person who got shot.

Jenkins, the other eyewitness, said the victim was an innocent bystander. Interim Police Chief Howard Jordan said at a news conference that the victim may not have been involved in the dispute that broke out in the camp earlier.

A mood of shock and sadness settled on the assembled crowd as hundreds of people began to question what went wrong.

"Everyone is focusing on Occupy, but this guy has a family," said Todd Walker, a resident who works with troubled Oakland youth, "Everyone is worried about a patch of grass, but the problem is too many murders in Oakland."

Other long-time camp residents say the shooting was was unrelated to the tent campers. "The only Occupy Oakland relationship here is that our medics were the first to arrive on the scene," said Verucha Peller, an activist who has been around the camp since the beginning.

Shortly after the shooting, several people began to place votive candles nearby.

Meanwhile, in Berkeley, the UC campus was relatively quiet for much of the day Thursday, but protesters were debating whether to set up their camp in front of Sproul Hall again. Previous attempts on Wednesday brought immediate responses from police in riot gear.

Campus police, aided by Alameda County sheriff's deputies, had arrested 40 people by Thursday afternoon, including 32 students, one professor and seven people not affiliated with the campus. Most were arrested Wednesday, but one man was detained Thursday morning after setting up a tent on the steps in front of Sproul Hall.

Students and professors reacted angrily Thursday to the previous evening's police response, saying officers used too much force against nonviolent protesters, who joined arms and blocked access to the encampment. But police and campus officials said they had given demonstrators ample time to remove their tents, and they said the resistance to police orders could not be considered a nonviolent protest.

"The campus is not a campground, and we will do our best to enforce the rules and regulations," said UC police Chief Mitch Celaya. "When people are chain-linked together and are not complying, they make it hard on the officers."

Celaya's comments came as videos and photographs of the police actions made their way around the Internet, inflaming protesters at other Occupy sites around the country.

Twitter users condemned the police response, much as they had when Oakland police used tear gas and beanbag rounds to crack down on demonstrators at Occupy Oakland last month.

The reaction illustrated the ongoing debate over how the university deals with civil disobedience. Last year, a campus panel issued a scathing report criticizing administrators and police for their response to a November 2009 protest at Wheeler Hall; 46 people were arrested at the demonstration, and one woman's fingers were broken by a police baton.

Earlier this week, the Berkeley City Council refused a mutual-aid police agreement with UC Berkeley, citing the university department's handling of previous demonstrations as a reason not to help out on campus.

The sheriff's department responded to Wednesday's demonstrations as part of its own mutual-aid pact with the university, said Sgt. J.D. Nelson, a department spokesman.

"This is UC Berkeley's gig," he said. "At some point, they're going to go in and complete their task, whatever their task is, and we go in and help them achieve that."

Listen to Tribune reporter Angela Woodall's SoundCloud recording of Mayor Quan's press conference Thursday after the fatal shooting:

Staff writers Josh Richman, Thomas Peele and Doug Oakley contributed to this story.