This post has been updated. Read an update on veteran Scott Olsen’s current condition here.

Following the violent clashes that broke out between police and Occupy Oakland protesters last night, some have started to questions the level of force used.

Occupy Wall Street protesters run from tear gas deployed by police at 14th Street and Broadway in Oakland Tuesday. (Darryl Bush/AP)

In a statement, police said they fired canisters of tear gas and bean bag rounds at protesters, but denied they used flashbangs or rubber bullets.

Protesters say police are lying about their use of force, posting photos of welts on Twitter to prove rubber bullets were used, and slow-motion videos of the clashes on YouTube they say shows that police used flashbangs.

Below, Jen Lasher tweeted a photo of a welt she says was caused by a rubber bullet:

Veteran For Peace says one of its members, Scott Olsen, a Marine Corps veteran twice deployed to Iraq, is now in the hospital with a fractured skull, “struck by a police projectile fired into a crowd” in Oakland this morning.

Oakland protester Schuyler Erle tweeted a photo of what he said was a rubber bullet found in downtown Oakland:

Sam Rosenfeld, chairman of the Densus Group, an international crowd management consulting firm, said in a phone interview that if the photos are legitimate, police clearly used shotgun shells full of hard rubber on the protesters.

In the following video, which is slowed down for effect, protesters say it’s clear police also used flashbangs:

A flashbang is a stun grenade that produces a loud blast and is used to disorient a person’s vision and other senses. Although flashbangs are designed to be non-lethal, several people have died in the past after being hit by them.

Based on the video, Rosenfeld also says it’s possible flashbangs were used.

In a statement about the clashes, Oakland police said that they did not use rubber bullets or flashbang grenades, but cannot speak for the other law enforcement agencies on the scene.

The police said they did use “less than lethal” force on the protesters. Less than lethal force is used by police for the purpose of suppressing protests that become violent.

In this case, police say the less than lethal force they used was bean bag rounds, which are baton rounds fired from a shotgun. While bean bag rounds look harmless (much like a tiny beanbag), the birdshot inside and speed at which they are fired causes people who received the shot to have intense muscle spasms that briefly renders their bodies immobile.

“Police fired approximately four bean bag rounds at protesters to stop them from throwing dangerous objects at the officers,” the police statement said.

Oakland protester Erle tweeted a photo of the bean bag rounds used:

The Oakland Police Department’s crowd management policy explicitly bans the use of bean bags.

Finally, police and protesters disagree on whether CS smoke, or tear gas, was used.

“In the footage you can see that after something is dispersed, not only the protesters react but also media crews, bystanders, and those who weren’t protesting,” Rosenfeld says. “They were all being affected. This indicates it could have been CS smoke. However, police also use smoke on its own to simulate CS smoke to prompt a psychological reaction.”

Erle also tweeted a photo that Rosenfeld says is clearly a CS canister:

Police say they were in the right to use bean bag rounds last night because protesters had thrown M-80 explosives, paint, and other hazardous materials at them. Reporters at the scene said protesters were throwing objects at the police.

Rosenfeld says Occupy Oakland protesters are “significantly more militant” than all the other Occupy protests. “The other protesters have a cooperative relationship with authorities, which is why Occupy Wall Street has been allowed to stay in the park in New York. But Oakland has refused to cooperate.”

This is not the first time the Oakland police force has been accused of using excessive force. This month, the San Francisco Chronicle reports the city of Oakland agreed to pay a $1.7 million settlement to the family of Jerry Amaro, who died in 2000 after police used excessive force during his arrest on suspicion of buying drugs.

In 2009, protests broke out after a white officer, Johannes Mehserle, was convicted of involuntary manslaughter in the 2009 shooting of Oscar Grant, an unarmed black man, at a BART train station in Oakland, Calif. Demonstrators called it a lack of justice.

Occupy Oakland has agreed by consensus not to cooperate with the Oakland Police Department under any circumstances, and instead formed its own internal police force.

Occupy Oakland planned to regroup Wednesday night for a general assembly meeting at 6 p.m. in Oscar Grant Plaza.

In a message, the group wrote: “Meet at 14th & Broadway. Find your friends and stay safe.”