FOLSOM, Calif. (CBS13) — Four officers suffered minor injuries in a sudden attack by a group of inmates in a CSP-Sacramento yard, authorities said.

Three correctional officers and a correctional sergeant were checking inmates from the prison’s B Block for weapons before releasing them into a maximum security yard when the attack took place just after noon, according to prison officials.

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It is not known how many inmates were involved in the attack. Investigators are reviewing surveillance footage to identify all of the participants.

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All four victims were taken to the hospital and treated for minor injuries.

Their identities have not been released.

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An earlier draft of this article incorrectly identified the prison as Folsom State Prison instead of California State Prison, Sacramento.