(AP) -- New York state officials say employees at a maximum security prison fell ill after a letter containing suspected fentanyl was opened.

Gov. Andrew Cuomo says 11 people were taken to a hospital Friday from the Clinton Correctional Facility Annex in Dannemora.

State police say they are in stable condition.

An investigation by the state police and Department of Corrections and Community Supervision is ongoing.

The Annex is on the grounds of the Clinton Correctional Facility.

The prison is known for the escape of two of inmates that was dramatized in the miniseries “Escape at Dannemora.”