A prison warden was knocked unconscious when prisoners clashed with staff at a prison in Northern Ireland.
Two others were injured when they were attacked at Maghaberry, near Lisburn, Co Antrim.
The trouble flared last night after three prisoners refused to return to their cells after using pay phones.
The officer who was knocked out hit his head on a pillar.
One officer received cuts behind his ear.
A Northern Ireland Prison Service spokesman said today that the prison's governor, Pat Maguire, had launched an internal investigation into the incident.
Meanwhile, the search for a new director general of the prison service has started.
Applications for the job to replace Colin McConnell close on 4 May.
The post carries a salary of up to £160,000.
Mr McConnell is moving at the end of next month to head the Scottish Prison Service.
