A number of prison officers have been taken to hospital after violence broke out at a young offenders institute.
The disturbance took place on Friday lunchtime at Feltham Young Offender Institute in west London and has left 14 staff members requiring hospital treatment.
The Ministry of Justice confirmed there were no serious injuries and the incident was brought under control "within 25 minutes".
However, it is not clear how many people were involved.
A Prison Service spokesman said: "An incident at Feltham Young Offender Institute was quickly resolved by our brave and diligent prison officers.
"We will never tolerate violence against our staff and will punish those involved."
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Around 100 boys and young men aged between 15 and 21 are held at Feltham Young Offender Institute.
An inspection report published in June identified soaring levels of violence and self-harm, high use of staff force, poor care and long periods of lock-up in cells.
And in October, inspectors found the safety of the prison had dropped to an "appalling" level over the first half of the year.
According to the inspectors' report, there was a 45 percent rise in violent incidents over six months, while cases of self-harm had tripled.