SAN QUENTIN -- A lock down at San Quentin prison ended early Thursday, but the underlying tensions caused by an escalation of gang violence remained in the aging and overcrowded state facility.

The lock down began after a prison guard in the toughest section of Death Row was severely slashed Wednesday, forcing the lock down of the entire prison and the removal of inmates to cages in the exercise yard.

Inmate Richard Penunuri, 27, slashed the officer's lower left arm with a homemade razor-like weapon when the guard was removing the inmate's handcuffs in his cell around 10:45 a.m., said Terry Thornton, spokeswoman for the California Department of Corrections and Rehabilitation.

Sgt. Eric Messick said officials searched the prison for weapons between 2 p.m. and 10 p.m. Wednesday and recovered a needle-like projectile.

Meanwhile, Penunuri has been confined to his quarters as are the rest of the approximately 100 inmates in the adjustment center. Those inmates will not have yard exercise and their movements will be confined to emergency or priority medical or dental appointments, Messick said. Visiting is also prohibited.

"They should thank their lucky stars they are in an American prison," Messick said.

There will be an administrative investigation, a rule violation report will be issued and a hearing will be held regarding the attack, Messick explained. Penunuri could be assessed an additional 10-day confinement to quarters and loss of store privileges if it's determined he slashed the guard.

"Since he was the sole person in the cell, there seems to be no question who did it," Messick said.

Penunuri already has the lowest level of privileges, Messick said.

The injured officer, who has not been identified, was taken to a Marin County hospital where he received more than 30 stitches to seal a gash that went "nearly down to the bone," Thornton said.

The prison immediately went on lock down after the attack.

Inmates in the 'bad boy' section of Death Row's adjustment center were removed from their cells and taken to individual holding cages in the exercise yard by an emergency response team.

The assault was a 'planned attack', prison officials said, in retaliation for actions taken over the weekend against members of the infamous Cole Street Gang. Members of the gang barricaded themselves in their Death Row cells and had to be forcefully removed.

Penunuri, who was condemned to death in 2001 in Los Angeles County for killing two people and ordering a hit on a witness at his trial, was housed in the prison's adjustment center for inmates with a history of disciplinary problems, Thornton said.

Wednesday's stabbing follows an inmate riot less than two weeks ago that broke out at a San Quentin dining hall, injuring two staff members and more than 20 inmates. Inmates were slashed and stabbed with homemade weapons, including toothbrushes that had been filed to points or with razors melted into the heads.