The inmates were found at Kirkland Correctional Institution in the capital city of Columbia, Department of Corrections Director Bryan Stirling told The Associated Press. Stirling did not say how they died or release any further information.
Stirling said he asked the State Law Enforcement Division to assist Corrections police with their investigation. Coroner Gary Watts confirmed he was investigating four deaths at the facility, but wouldn't give any details about how the inmates died.
Kirkland operates a specialized housing unit for the state's most dangerous inmates, an assessment and evaluation center for new inmates sentenced to more than three months, and a 24-bed infirmary, according to the Corrections website. The prison has been the scene of previous violence. In 2015, two inmates held two nurses hostage with homemade knives for seven hours after forcing their way into a nursing station where prescription drugs were kept. One nurse's throat was cut, but she survived.
Their cases are still pending.