The Government says it has ruled out a public inquiry into the 1998 Real IRA Omagh bombing which killed 29 people.
The Co Tyrone blast was one of the worst atrocities in the Northern Ireland conflict and relatives have called for an all-Ireland probe into whether the authorities could have done more to prevent it.
Northern Ireland Secretary Theresa Villiers said: “I do not believe that there are sufficient grounds to justify a further review or inquiry above and beyond those that have already taken place or are ongoing.”
Twenty-nine people, including a woman pregnant with twins, died when the dissident republican car bomb ripped through the town just months after the signing of the historic Good Friday Agreement peace accord in Northern Ireland.
While no one has been criminally convicted of the crime, four republicans were found liable for the atrocity in a landmark civil case taken by some of the bereaved relatives and ordered to pay £1.6 million compensation.
Last month families of some of the victims outlined details of an independent report they commissioned into alleged intelligence failings on both sides of the border in the lead up to the atrocity and with the subsequent criminal investigations.
Ms Villiers said it was not an easy decision to make and all views were carefully considered. She said: “I believe that the ongoing investigation by the Office of the Police Ombudsman for Northern Ireland is the best way to address any outstanding issues relating to the police investigation into the Omagh attack.
“The fact remains that the Real IRA carried out the bombing in Omagh on 15 August 1998, murdering 29 people and injuring many more. Responsibility is theirs alone. I sincerely hope that the ongoing police investigation will bring to justice those responsible for this brutal crime.”
Relatives of some of the victims, who claim the 1998 Real IRA attack could have been prevented but for intelligence failings, reacted with fury to the decision.
Michael Gallagher, whose son Aiden, 21, was among the victims, said: “Over a year ago we gave this Government a report which showed that state agencies had failed and 31 people had died and 250 were injured unnecessarily.”
But Mr Gallagher described the reasons given by Ms Villiers for ruling out a public inquiry as “trivial” and told Sky News victims’ families would be mounting a legal challenge to the decision.