OKMULGEE COUNTY, Oklahoma - State agents are investigating an assault at the Okmulgee County Jail. 

The inmate’s family says he was flown to St. Francis Hospital for treatment by flight medics from the jail.

Few details have been released, but the Oklahoma State Bureau of Investigation is now investigating.

Christian Hill, 25, is hooked up to machines at Saint Francis Hospital in Tulsa. 

A spokesperson from OSBI says, quote, "We were requested by the District Attorney to investigate an inmate assault. The injuries are severe."

The OSBI says the agency was called Monday, the day after Hill was assaulted, which is not uncommon in these types of situations. 

State investigators also say agents are interviewing Hill and anyone who may have been seen what happened, including other inmates, deputies and jailers.

They'll also check for surveillance video. 

This isn't the first time an inmate at the Okmulgee County Jail has been hospitalized. 

In 2014, officials say a fight led to burned mattresses, broken glass, barricaded units and flooding after an inmate got upset about being transferred. 

The jail director blamed it on overcrowding issues since 323 inmates were being housed that day, nearly 100 more than its approved to house.

Hill's condition is unknown at this time. His family has an attorney. 

News On 6 reached out to the jail, sheriff's office and District Attorney for more information but didn’t hear back.