There is a security alert at Maghaberry Prison near Lisburn in Co Antrim.
The incident began after dissident republican prisoners barricaded themselves into a dining room in the Roe House wing of the jail.
A spokesman for the Northern Ireland Prison Service said the incident arose when between 20 and 30 separated republican prisoners barricaded themselves into the room following mass this morning.
British army technical officers were called to the wing after a suspicious object was found in a corridor outside the dining room. The officers dealt with the object and declared the area safe.
A number of the republican prisoners remain in the dining room.
Visits to the prison have been suspended because of the security alert.
