The South Dakota State Penitentiary in Sioux Falls is on lockdown.
The Department of Corrections said the lockdown includes the Jameson Annex, the prison’s maximum security facility.
Department officials did not say what prompted the lockdown, nor did they say how long it will last. It went into effect Sunday night.
DOC staff are managing inmates’ phone service during the lockdown, and most visits are being cancelled. The exceptions are for previously scheduled visits and attorney meetings.
"Because this is related to facility security and operations, we will not be responding to further questions and inquiries during the lockdown," a statement from the DOC said. "If the release of additional information is warranted, the information will be provided on the agency website and social media channels."