Mercer was assaulted at HMP Moorland in Doncaster
The teenager who murdered schoolboy Rhys Jones has been attacked in jail, the Prison Service has confirmed.
Sean Mercer, 18, was assaulted at HMP Moorland in Doncaster, South Yorkshire, but the incident was stopped by the "timely intervention" of staff.
Mercer and another inmate suffered minor injuries in the incident on 27 December and neither required hospital treatment, said the Prison Service.
Mercer, of Croxteth, Liverpool, was jailed for 22 years last month.
He was 16 when he shot Rhys outside the Fir Tree pub in August 2007, as the 11-year-old walked home from football practice.
During his trial, Liverpool Crown Court heard Mercer was a member of the Croxteth Crew gang, which terrorised the local community and was involved in a long-running and bloody feud with the Strand Gang, based on the neighbouring Norris Green estate.
Mercer was firing a gun at one of the Strand Gang when a bullet hit Rhys in the neck.
The schoolboy died in his mother's arms soon afterwards.
A Prison Service spokeswoman said: "We can confirm an incident took place at HMP Moorland at 2.30pm on Saturday, December 27, in which two prisoners assaulted each other.
"The incident lasted less than two minutes and was quickly resolved by the timely intervention of staff."