BISMARCK, N.D. (AP) – Correction officials say the North Dakota State Penitentiary is on lock down because of two separate assaults on staff members.

Seven employees were referred to a doctor following the assaults at the maximum-security prison. The Department of Corrections and Rehabilitation did not provide specifics about the assaults, which are under investigation.

Corrections officials say they will review the lock down on Monday. Visitation, either in person or by video, is banned during a lock down.