An inmate at U.S. Penitentiary, Atwater, suffered "non-life-threatening" injuries early Thursday and a staff member also suffered a minor injury during an incident, prison officials reported.
Few details were available. Neither the inmate nor the staffer were identified.
In a brief statement issued Thursday afternoon, prison officials said "multiple incidents" were reported inside the prison around 7 a.m. The unidentified inmate and staff member were taken to an area hospital for treatment.
"All inmates were returned to their assigned housing units and secured," officials said in the statement. "The institution is currently on modified operations status."
The FBI was notified and the incidents were under investigation Thursday.
"At no time was the public in danger, and the institution will return to normal operations as soon as possible," officials said.
USP Atwater houses 1,162 male inmates.