Officers from the North East counter-terrorism unit are investigating the attack on two prison officers at Full Sutton maximum security jail near York.
It is understood that three inmates held one warder hostage for a number of hours.
In a statement, the Chief Executive of the National Offender Management Service, Michael Spurr, said:
“At 4.25pm on Sunday 26th May, a prison officer was forcibly taken hostage by three prisoners at HMP Full Sutton. None was serving a sentence for terror-related offences.
A second officer immediately attempted to come to her colleague’s aid and was injured as a result, receiving cuts to her arm.
The incident concluded at 8.40pm, after specially trained prison staff intervened to release the officer.
The officer taken hostage suffered a broken cheekbone and a number of wounds to his face and neck at the beginning of the incident.
Both members of staff were treated in hospital for their injuries.
This was a serious incident and my first thought is with the officer who was taken hostage – we will do all we can to help him recover from this experience.
I want to commend all staff involved for their great courage and professionalism.”
The statement also confirmed that neither of the staff involved is ex-military.
The three prisoners involved are Muslim. Two of the prisoners are 25 and one is 26.
More top news
A poll carried out this week found roses are still the preferred choice for two thirds of people on Valentine's Day.
The 'Teensleep' project is looking at how more and more youngsters are not getting enough sleep, often because they're glued to technology.
While all other regions saw life expectancy for men improve - the North East was the only region where male life expectancy went down.