The man who kept Amanda Berry and two other women captive for more than a decade in Ohio has been found dead in prison.

Ariel Castro, 53, was discovered hanging in his cell by prison staff, and medical personnel were unable to revive him. He was later taken to the prison's medical facility, where he was pronounced dead.

"He [Castro] was housed in protective custody which means he was in a cell by himself and rounds are required every 30 minutes at staggered intervals" said a spokesperson for the Ohio Department of Rehabilitation and Correction.

"Upon finding inmate Castro, prison medical staff began performing life saving measures. Shortly after he was transported to [medical facility] where he was pronounced dead at 10:52 pm."

The spokesperson said Castro was held in protective custody due to the grave nature of the case. He was not on suicide watch. Authorities have promised a probe into the incident.

Castro had been sentenced to life imprisonment for kidnapping Berry, Michelle Knight and Gina DeJesus and keeping them captive for 10 years at his Cleveland home, where he raped them repeatedly and even fathered a child with Berry.

The women were freed after Berry escaped in May and made a dramatic phone call to police. Castro was arrested on the same evening.

He pleaded guilty to 937 counts of kidnapping and rape charges. He was sentenced to life in prison plus 1,000 years, with no chance of parole, in August.

Ohio kidnappings