Northern Ireland fire crews were forced to put a number of fires at the high-security Maghaberry Prison in County Antrim.
No-one was injured after small fires broke out in a dining room and the wings of the prison complex last night.
The incident comes just one week after a number of inmates staged a rooftop protest over cell space at the jail.
Mr Finlay Spratt of the Prison Officers Association said he was not surprised there had been another incident at the jail.
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He said the organisation had been warning the management for months that incidents like this could take place.