James Bulger was murdered on Merseyside in 1993
James Bulger's killer Jon Venables was recalled to prison because of "extremely serious allegations", Justice Secretary Jack Straw has said.
He was released in 2001 on licence with a new identity after serving eight years for the murder of the toddler on Merseyside in 1993.
A report in the Sun newspaper claims Venables, now 27, is alleged to have committed a serious sexual offence.
Mr Straw is to meet James's mother to discuss the recent developments.
Venables and Robert Thompson - both aged 10 - became the UK's youngest murderers after abducting the two-year-old from a shopping centre in Bootle, Merseyside.
'Right to know'
Since the news broke that Venables breached his licence and had been returned to jail, ministers have refused to release details of his alleged offence.
On Wednesday, the Home Secretary Alan Johnson said he believed the public "had a right to know".
Jon Venables was released from prison under licence conditions
But Justice Secretary Jack Straw, appearing to overrule the minister, insisted that secrecy was in the public interest - and he was later backed by the prime minister.
In a statement issued by the Ministry of Justice, Mr Straw said: "I was unable to give further details of the reasons for Jon Venables' return to custody, because it was not in the public interest to do so.
"Our motivation throughout has been solely to ensure that some extremely serious allegations are properly investigated and that justice is done."
The BBC's Home Affairs correspondent, Danny Shaw, said government solicitors attempted to prevent The Sun publishing full details of the allegations against Venables.
Government sources have also told the BBC that James's mother, Denise Fergus, will not be told why he is back in jail.
Mrs Fergus told the Daily Mail she was angry that the Parole Board had not told her that her son's murderer had been returned to custody.
She said the authorities had broken their promise to keep her informed.
She told the paper: "Why can't the government be honest and tell us what he's done?"
Mrs Fergus, 42, accused the government of leading a "massive cover-up" because they did not want to admit that money spent on concealing Venables' and Thompson's identities had been "a complete waste".
She added: "All kinds of horrible thoughts were going through my head, and they still are because no one will tell me what he's done.
"It's wrong - as James's mother, I have a right to know."
Mrs Fergus said she had repeatedly asked for information about Venables' case during a meeting with a Probation Service officer.
"I threw question after question at her, but she blocked every one," she told the newspaper.
'Right to know'
Marie McCourt, from the charity Support After Murder and Manslaughter (Samm) on Merseyside, added her voice to those calling for Mrs Fergus to be told.
"If he is guilty of having broken those restrictions and/or committed any other serious offence then of course the family of the victim has a right to know," she said. "They above everybody have that right to know."
James Bulger's battered body was found by children playing on a freight railway line more than two miles from the shopping centre in February 1993.
Thompson and Venables were given life sentences, but released in 2001 with new identities and under certain licence conditions.
A court order prevents details being published which could reveal their whereabouts.