(Adds police seeking end to encampment, paragraphs 7-8

Former U.S. Marine Scott Olsen, whose injury during clashes between Oakland police and protesters last month galvanized the anti-Wall Street movement, has been released from the hospital, friends said Friday.

"He is out of the hospital as of yesterday or today, thank goodness," Adele Carpenter told Reuters.

Iraq Veterans Against the War spokeswoman Dottie Guy also confirmed Olsen's release to Reuters.

Olsen is focused on healing, Carpenter said. She added that "he is following the Occupy protests closely, as well as the vets' march against police brutality today."

Occupy Oakland organizers say Olsen, 24, was hit in the head by a tear gas canister fired by police during a downtown Oakland confrontation on Oct. 25. He was admitted to a local hospital in critical condition.

Acting Oakland Police Chief Howard Jordan has opened an investigation into the circumstances surrounding Olsen's injury but police and the city have not said how they believe the Iraq veteran was injured.

Police handed out notices on Friday to the Oakland protesters, warning they could be pushed out of their encampment, but demonstrators said they plan to stay.

The Oakland police union has called for the protesters to leave after a man was shot to death near their protest site on Thursday. But Occupy Oakland demonstrators denied the shooting, which took place at a public transit station at the edge of the downtown encampment at Frank Ogawa Plaza, had anything to do with their movement.

Olsen was released from in-patient care in time to celebrate Veterans Day, Carpenter wrote in a blog post on a website for the group Veterans for Peace.

The Iraq veteran was "still struggling with speech, but is attempting conversations without having the writing instrument out," on which he had been relying to communicate, Carpenter said in the blog post.

Word of Olsen's injury reinvigorated the Occupy Wall Street movement against economic inequality across the country, and shifted its focus to Oakland from New York.

Activists in Oakland and elsewhere took to the streets following his hospitalization, holding candlelight vigils and marches.

Olsen served two tours in Iraq, working as a technician and earning a handful of service medals.

Friends say he soured on military life after leaving the service and started a now-defunct website called "I hate the Marine Corps" that served as a forum for disgruntled servicemen.

Olsen received an "administrative discharge" from the service in late 2009, his uncle George Nygaard has said, although the precise reasons for it have not been confirmed.

Such a discharge can result from any number of behavioral or disciplinary issues. (Reporting by Mary Slosson in Los Angeles, additional reporting by Noel Randewich in Oakland; Editing by Greg McCune, Tim Gaynor and Eric Walsh)