A 15-year-old boy has died after being found unconscious in his cell at a young offenders institution in Kent.
The Prison Service said Alex Kelly had been identified as being at risk of suicide or self-harm, but did not give details of the boy's condition when he was found.
Kelly was taken to hospital from HMP Cookham Wood, near Rochester, but he later died, a spokeswoman said.
He had been serving a 10-month sentence for burglary and theft from a vehicle.
The teenager was found in his cell at about 20:30 GMT on Tuesday.
Staff tried to resuscitate him and paramedics attended before he was taken to hospital, but he was pronounced dead at 19:30 GMT on Wednesday.
'Lessons to learn'
Kelly is the second young offender to die within a week at young offenders institutions in the UK.
Jake Hardy was found at Hindley young offenders institution in Wigan on Friday and taken to hospital, where he died on Tuesday.
The Prison Service spokeswoman said: "Every death in custody or the community is a tragedy for families and has a profound effect on staff and other offenders.
"The National Offender Management Service (Noms) is committed to reducing the numbers of deaths in custody.
"Each death is subject to an investigation and, since 2004, these have been undertaken by the Prisons and Probation Ombudsman.
"Additionally, for young people who die in custody there will be a serious case review, commissioned by the local safeguarding board."
'Lack of resources'
A spokeswoman for the Prisons and Probation Ombudsman (PPO) said investigators would try to answer any questions Kelly's friends and family may have, and would also involve them in the investigation if they wished.
She said: "Our independent investigation will aim to identify the full circumstances of the death and whether there were any failings in Alex Kelly's care.
"Where possible we will identify lessons to be learned and make recommendations to the Prison Service to help prevent similar deaths in future."
Juliet Lyon, director of the Prison Reform Trust campaign group, said: "Lessons must be learnt from the tragic deaths within one week of two children in prison.
"Above all, we need to become 'wise before the event' and avoid locking up our most vulnerable young people in our bleakest institutions."
She also said that low staffing levels and lack of resources made it very difficult for staff to respond to youngsters in extreme distress.
Andrew Neilson, director of campaigns at the Howard League for Penal Reform, said the prison had a "chequered past".
"The last inspection report found the prison to be unsafe. So why do we continue to send children there, and places like it?," he said.
"The truth is that warehousing children in large prisons is completely inappropriate and ignores the fact that young people in conflict with the law often present many complex needs that a prison simply cannot provide for."