COLUMBIA, N.C. (AP) - Authorities have charged two more inmates at a North Carolina prison with drug offenses.

The Tyrrell County Sheriff's Office told local media outlets that 40-year-old Xavier D. Johnson and 25-year-old Jahmel J. Ross, who are being held at the Tyrrell Prison Work Farm, are charged with possession of controlled substances on prison or jail premises.

Sheriff Darryl Liverman says 30 inmates at the prison work farm have been charged with drug offenses since May. Officials say an investigation is continuing.