Soham murderer Ian Huntley is being treated in hospital after taking a suspected overdose.
A British Prison Service spokeswoman said an investigation was underway into events at Wakefield high security prison.
The killer was thought to have taken an overdose of prescription medication but his condition was not thought to be life threatening.
Huntley was jailed for 40 years for the murders of Holly Wells and Jessica Chapman, both 10, in Soham, Cambridgeshire, in August 2002.
At the 2003 trial of the former secondary school caretaker and his then girlfriend Maxine Carr it emerged that he had met the two girls as they walked past his home.
He then enticed them inside and killed them before hiding their remains.
Since being in prison Huntley has attempted suicide on at least two other occasions.
His first bid to take his own life happened while he was on remand at Woodhill jail in Milton Keynes in 2003. He had stored 29 pills in a box of tea bags.
The last recorded suicide bid took place in September last year. On that occasion, Huntley had to have his stomach pumped and was put under heavy sedation after being found unconscious and taken to Pinderfields Hospital in Wakefield, West Yorkshire.
While in prison, Huntley has also been subjected to attacks from fellow inmates. In October last year he was held at knifepoint after being ambushed on his way back to his cell following a meal, it was reported at the time.
PA