"Our staff do an incredible job in some very challenging circumstances to keep New Zealanders safe," Aben said.
"Assaults on our staff are unacceptable.
"Every assault on a member of our staff is taken seriously and any prisoner who resorts to violence is held to account."
She said it was a reality that the threat of violence couldn't be eliminated entirely - more than 75 per cent of the prison population have convictions for violence in their offending histories.
"But we do everything possible to minimise this risk.
"We have invested significantly in training and tools to keep our people safe."
This included tactical skills such as de-escalation, the introduction of stab-resistant body armour, on-body cameras and the expanded use of pepper spray.
She said staff and prisoners who had been assaulted were also provided support in reporting the incident to police, who determine whether charges are laid or not.