Counter-terrorism police are investigating after two inmates launched an attack on prison staff at a maximum security jail.
A Prison Service spokesman said five employees were taken to hospital after the incident on Thursday, which began when the two inmates assaulted a prison officer.
The situation was "quickly resolved by brave staff" at the 458-capacity HMP Whitemoor in Cambridgeshire, the spokesman added.
He did not state the nature of the injuries to the officers amid reports the inmates were wearing fake bomb vests and carrying improvised weapons.
The spokesman said: "Five members of staff at HMP Whitemoor attended hospital following a serious assault on an officer by two prisoners on January 9.
"The incident was quickly resolved by our brave staff and our thoughts are with the injured officers at this time.
"We do not tolerate assaults on our hardworking officers and will push for the strongest possible punishment.
"We have referred the incident to the police and it would be inappropriate to comment further at this time."
The incident is being investigated by counter-terrorism officers and no arrests have been made, the Met Police said.
A spokesman said: "Due to certain circumstances relating to this incident, it was deemed appropriate for the investigation to be carried out by officers from the Met Police Counter Terrorism Command.
"However, we must stress that at this early stage of the investigation we are keeping an open mind with regards to any motives and inquiries to establish the full circumstances of the incident are ongoing."
