A child murderer has been killed in Worcestershire's Long Lartin Prison, the Ministry of Justice has said.
Two prisoners are being held in police custody after the death of Subhan Anwar, who was jailed in 2009 for torturing and killing a two-year-old girl.
Anwar is understood to have been held hostage in his cell at the Category A jail before he was killed.
A Prison Service spokeswoman said: "An incident at HMP Long Lartin on Thursday February 14 resulted in the death of prisoner Subhan Anwar.
"Two prisoners are now in police custody and the matter is being investigated by police."
A West Mercia Police spokesman said: "West Mercia Police has launched a murder investigation after a 24-year-old man died in Long Lartin prison last night.
"The body of the man was found by prison officers just before 8pm on Thursday, February 14.
"Two men aged 47 and 45 have been arrested on suspicion of murder and are currently in police custody."
Anwar was jailed for a minimum of 23 years for the murder of his partner's daughter Sanam Navsarka.
His partner Zahbeena Navsarka was cleared of her daughter's murder but found guilty of manslaughter and jailed for nine years.
Anwar and Navsarka, from Huddersfield, West Yorkshire, were condemned for their cruel and selfish treatment of Sanam.
The violence inflicted on the youngster happened near the end of her life.
Anwar and Navsarka, from Huddersfield, West Yorkshire, tried to claim Sanam had stopped breathing after they left her alone in the bath for 10 minutes.
But she was found to have 107 separate external injuries when she died.
Her tiny hand prints and bloodstains were found inside cupboards at the home in Huddersfield and also at a former property in Batley, West Yorkshire.
Both of her thigh bones had been fractured, causing fatty deposits to enter her bloodstream and resulting in her death, and she had fractures to both of her arms.
As well as putting her in a tumble dryer, Anwar dumped her in the bin as her mother looked on.
Long Lartin is a maximum security prison near Evesham, which holds up to 622 inmates who must be serving a minimum sentence of four years.
In a January 2012 report, chief inspector of prisons Nick Hardwick revealed that two rows of individual "bleak cages" were being used as a grim exercise yard for segregated inmates at the prison.
He said the cages were "not fit for purpose" and their use was unacceptable.
In August 2011, child killer Andrew Randall, who tortured and sexually abused his seven-week-old daughter Jessica, had his throat slashed by fellow inmates at Long Lartin but survived.