A demonstrator waves a flag as rubbish burns at the Occupy Oakland demonstration in Oakland, California, November 3, 2011. Police in riot gear clashed with protesters in Oakland in the early morning hours on Thursday, firing tear gas to disperse demonstrators lingering in the streets after a day of mostly peaceful rallies against economic inequality and police brutality. [Photo/Agencies]

SAN FRANCISCO - A former US Army Ranger and Occupy Oakland protester was in intensive care on Friday after a veterans' group said he was beaten by police during clashes with anti-Wall Street demonstrators this week.

Kayvan Sabeghi, 32, was arrested and hospitalized about a week after another US military veteran, former Marine Scott Olsen, was badly injured in a confrontation with police that helped spark the latest round of unrest.

The group Iraq Veterans Against the War said Sabeghi was detained during disturbances that erupted late on Wednesday in downtown Oakland and was charged with resisting arrest and remaining present at the place of a riot.

Police arrested more than 100 demonstrators in clashes with protesters late on Wednesday and early on Thursday following a day of mostly peaceful rallies against economic inequality, corporate excesses and bailouts of major banks.

Several bank branches were closed and the Port of Oakland was shut down for several hours by the demonstrations.

Brian Kelly, who co-owns a brew pub with Sabeghi, said his business partner told him he was arrested and beaten by a group of policemen as he was leaving the protest to go home.

"He told me he was in the hospital with a lacerated spleen and that the cops had jumped him," Kelly said, adding that Sabeghi had served as an Army Ranger in Iraq and Afghanistan.

"They put him in jail, and he told them he was injured, and they denied him medical treatment for about 18 hours," he said.

The Oakland Police Department did not immediately return calls seeking comment.

The veterans' group said in a statement that police struck Sabeghi with nightsticks on his hands, shoulders, ribs and back, and that in addition to a lacerated spleen he suffered from internal bleeding.

Sabeghi's name was listed by the Alameda County Sheriff's Office as among those arrested that night, and Highland General Hospital confirmed he was a patient in its intensive care unit.

City officials have said that eight people -- five civilians and three police officers -- were injured in the late-night confrontations. But it was not immediately clear whether Sabeghi was among those counted as hurt.

Police had remained largely out of sight during Wednesday's protests until busloads of officers in riot gear moved in on demonstrators at about midnight, firing volleys of tear gas to disperse hundreds lingering near a downtown plaza used as a base camp for Occupy Oakland activists.

Police made a second charge with batons and tear gas about an hour later to drive protesters deeper into the square.

City officials said police had acted in response to small pockets of "anarchists" who vandalized property, set fires, assaulted police officers and broke into a downtown building.

Many protesters said that the streets were largely calm when police converged, although sporadic vandalism and unruliness had been reported during the day.

The call for a citywide strike that preceded the confrontations was triggered in part by outrage over Scott Olsen's injuries during a separate confrontation with police last Tuesday that became a rallying cry for the anti-Wall Street protest movement nationwide.