More than a dozen prison officers were taken to hospital during a rash of violence at a youth jail.
Some 20 staff at Feltham Young Offenders Institution (YOI) were injured in separate incidents over the weekend, the Prison Service said.
The perpetrators will face adjudication hearings over the next few days and could face prosecution by police.
The head of the Prison Officers’ Association (POA) said the violence was “unacceptable” and it would push for prosecutions.
We will never tolerate violence against our staff and will push for the strongest possible punishment. Prisons Service
A Prison Service spokeswoman said: “A completely unacceptable series of assaults on staff at Feltham over the weekend led to 20 officers receiving injuries – with 13 needing hospital treatment.
“Our sympathies are with those hard-working and committed staff, who deserve to be able to carry out their jobs without facing this kind of behaviour.
“We will never tolerate violence against our staff and will push for the strongest possible punishment, which could lead to them spending more time behind bars.”
It is understood the injured officers have since been discharged from hospital.
Mark Fairhurst, national chairman of the POA, tweeted: “The violence against staff at HMP Feltham over the weekend is not acceptable.
“Replace the term ‘children’ with ‘violent young criminal’ and you more accurately describe what @POAUnion members in the juvenile estate face.
“We will support staff and push for prosecutions.”
Wishing the 22 staff at HMP Feltham who got viciously assaulted by the âchildrenâ at the weekend a speedy recovery. Well done to all @POAUnion members there today for your solidarity with a strong committee. Great to see a caring Governor work with the POA to ensure all are safe.— National Chair POA (@POAnatchair) April 8, 2019
The POA called for a meeting with Justice Secretary David Gauke over “sickening” and “out of control” violence against prison staff.
Steve Gillan, the association’s general secretary, said: “The Secretary of State Mr Gauke needs to step up and take responsibility.”
Feltham YOI is made up of two parts – Feltham A, which holds 15 to 18-year-olds, and Feltham B, which holds young adults aged 18 to 21.
In its A unit there is capacity for 180 young people, while 360 young adults can be held in unit B.
Once judged to be unsafe, an inspection last year found levels of violence had been cut at the YOI.
Safety had improved “quite dramatically” after new measures were introduced that included the teenagers being rewarded for good behaviour – including being given sweets and chocolate.
But the facility has faced a battle to keep gang rivalries in check after “postcode” allegiances caused conflict among inmates.
In March Feltham’s independent monitoring board said the issue presented staff with an “enormous problem”.
Assaults on jail staff have surged to record levels after a safety crisis swept through much of the prisons estate in England and Wales.
The Ministry of Justice pointed to a number of measures implemented since the start of last year, including the roll-out of PAVA spray, the recruitment of thousands of additional officers and the introduction of more dog units, search teams and scanners to stem the flow of drugs that fuel much of the violence behind bars.
Ministers have also brought forward legislation that doubles the maximum prison sentence for assaulting a prison officer, from six to 12 months.