A DUP MLA has called for a review of staffing levels at Maghaberry Prison after a warder was knocked unconscious.
The officer hit his head on a pillar during clashes with inmates on Wednesday night.
Two others were injured in the trouble which flared after three prisoners refused to return to their cells after they had been using pay phones.
A spokesman for the Prison Service said that the jail’s governor Pat Maguire has launched an internal investigation into the incident.
The DUP’s Paul Givan, who chairs the Assembly’s justice committee, raised concerns over staffing at Maghaberry and claimed officers had feared an attack.
“Any incidence where staff are attacked inside a prison is obviously very worrying and there have been warnings from prison officers that this situation might arise,” said Mr Givan.
“I share the concern of the officers around the number of staff which are present on the landings. I would pay tribute to the staff who were on duty, however, and for how they handled the situation.
“I believe that there should be a review of staffing levels in Maghaberry because it is vital that the safety and wellbeing of staff and prisoners is maintained.”
He added: “We can only be relieved that on this occasion the attack did not result in more serious injuries, but such incidents must not be allowed to happen again.”
UUP MLA Basil McCrea condemned the attack and called for tough sanctions against those responsible.
He said: “As a society we ask prison officers to deal with some extremely dangerous criminals on a daily basis, and this incident highlights the very real physical risks which they face on our behalf.”
Meanwhile, the search for a new director general of the prison service has started. Applications for the job to replace Colin McConnell – which carries a salary of up to £160,000 – close on May 4.
Mr McConnell is moving at the end of next month to head the Scottish Prison Service. The current deputy director, Max Murray, will act up until the position is filled.