The mother of murdered child James Bulger said the Parole Board had made the "wrong decision" by moving to release one of her son's killers.
Denise Fergus said Jon Venables had shown he was still "a danger to himself and to the public".
She received a call from the ProbationService telling her that Venables, now 30, had been cleared for release for a second time.
He returned to jail in 2010 after his parole was revoked, following the discovery that he had accessed indecent images of children. Venables admitted the offence and was jailed for a further two years.
He had previously been sentenced to life alongside Robert Thompson for the 1993 murder of 2-year-old James, who was beaten to death after being taken by Venables and Thompson, then both aged 10, from a shopping centre in Merseyside.
Both were released in 2001 and given new identities, with a legal ruling ordering that new photographs of them should not be published. Thompson has not been heard of since his release. Earlier this year, Fergus, and James' father, Ralph, both addressed Venables' parole hearing, calling for him to stay in prison.
"I've been fighting for justice for James for 20 years now and I will continue to do so. The Parole Board have made the wrong decision," Fergus said.
She had earlier broken the news of the decision on Twitter, adding: "Just don't believe what I've got to go through. Again."
A Ministry of Justice spokesman said: "The re-release of life-licensed offenders is directed by the independent Parole Board once they are satisfied they can be safely managed in the community. They may be recalled to prison at any time for breaching their licence conditions."
