Iraq war veteran is believed to have sustained damage to speech centre of his brain in injury at Occupy protest on Tuesday

Scott Olsen, the Iraq war veteran who was seriously injured by a police projectile during a protest in Oakland, has regained consciousness but "cannot talk".

Olsen, 24, is communicating with friends and family at his bedside by writing notes, but his injury is believed to have damaged the speech centre of his brain, according to Keith Shannon, who served with Olsen in Iraq.

Olsen is believed to have been injured by a police projectile. He was hit in the forehead in downtown Oakland on Tuesday evening, after marching with fellow demonstrators to protest the closure of an Occupy Oakland camp in the city.

"He cannot talk right now, and that is because the fracture is right on the speech center of his brain," said Shannon. "However, they are expecting he will get that back."

Shannon added that Olsen's "spelling is not near what it used to be".

"The doctors expect that he will have a full recovery," said Shannon, who is due to visit Olsen on Friday afternoon. "However, it is going to be a long road ahead for him."

Olsen was "really happy" to see his family, Shannon added.

A spokesman for Highland General Hospital confirmed Olsen could not talk, but said he "understands everything" doctors and family are saying. His family flew to be at his bedside on Thursday. The spokesman said Olsen remained under observation to determine if he needs surgery. His condition is "fair".

Video footage posted to YouTube shows Olsen lying motionless in front of a police line after apparently having been hit. A group of up to 10 protesters gather around him, but a police officer can be seen throwing a device close to the group which then explodes with a bright flash and loud bang, scattering the protesters. The video then cuts to footage of protesters carrying Olsen away as he bleeds from the head.

Oakland Mayor Jean Quan, who was in Washington DC when the clashes occurred, has sought to distance herself from the police action.

"I only asked the chief to do one thing: to do it when it was the safest for both the police and the demonstrators," she said.