Counter-terrorism officers have been brought in to investigate an attack on two prison officers at a maximum security jail.
A male warder was left with a broken cheekbone after being held hostage by three male prisoners, two aged 25 and one aged 26, while a female prison officer received minor injuries as she attempted to help her colleague.
The North East Counter Terrorism Unit (CTU) has been called in to lead the investigation into the incident at HMP Full Sutton in Yorkshire.
A statement from the unit said: "Inquiries are ongoing to establish the circumstances surrounding the incident. Given the potential nature of the incident and the range of skills and expertise within the North East CTU, the unit is leading the investigation at this time."
Both prison officers have received treatment for their injuries and have since been discharged.