An inquiry has been ordered into a disturbance at a high-security prison.
The BBC understands staff were attacked with pool balls during the disorder which involved 81 inmates at HMP Long Lartin in Worcestershire.
The disorder, which was resolved by 04:30 BST on Thursday, was contained within a single wing, with no injuries to staff or prisoners.
Justice Minister Sam Gyimah MP said an investigation was expected to take a “number of weeks”.
Speaking in the House of Commons, Mr Gyimah said: “The incident is, of course, of concern and we will need to properly investigate what drove the actions of a relatively small number of individuals.
“That will take a number of weeks to ensure all intelligence is properly examined and that we learn lessons and apply them to prevent any recurrence.
“We cannot speculate on the cause of this incident but we know the prison was running a full regime and that this was not linked to any shortfall in prison officer staffing levels.”
BBC home affairs correspondent Danny Shaw said he understood about 10 “Tornado teams” of riot officers were sent to the prison on Wednesday.
Eighteen prisoners have since been moved to other jails.
Long Lartin is one of the highest-security prisons in England and Wales, with two-thirds of the inmates serving life sentences.
Rob Preece, spokesman for the Howard League for Penal Reform, said the disorder was “concerning… not least because this is the latest in a long line of disturbances in prisons across the country, which is causing great distress to staff, to prisoners and their families”.
He added: “It will be particularly worrying for the Ministry of Justice because this is the first disturbance of its kind that we have seen in a maximum security prison.
“We do not expect to see disturbances like that in the high security estates and this will be giving a great deal of cause for concern .”
The disturbance follows riots at prisons including Lewes, Bedford, Birmingham and Swaleside.
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