An independent inquiry into the Omagh bombing will examine alleged security failings that led a High Court judge to conclude the outrage could plausibly have been prevented.
The UK government has outlined its terms of reference for the independent probe, which will be chaired by house of lords member Andrew Turnbull.
The dissident republican bomb exploded in the Co Tyrone town on August 15 1998, killing 29 people, including a woman pregnant with twins.
Northern Ireland Secretary Chris Heaton-Harris ordered the statutory inquiry into the attack last year in response to a court judgment that directed the Government to establish some form of investigation.
Michael Gallagher, whose son Aiden died in the Real IRA bombing, took the legal challenge that resulted in the Belfast High Court judge directing the state to act.
Mr Heaton-Harris outlined the terms of reference by way of a written parliamentary statement yesterday.
In his 2021 judgment, Mr Justice Horner directly recommended that the UK government carry out an investigation into alleged security failings in the lead-up to the atrocity.
While having no jurisdiction to order the Irish government to act on the matter, the judge urged authorities there to establish their own probe in light of his findings.
A number of families of Omagh victims have repeatedly called for an inquiry to also be carried out into the bombing in the Republic of Ireland. Mr Heaton-Harris has also pressed the Irish government to act.
On a visit to Belfast yesterday, Tánaiste Micheál Martin pledged to co-operate with the UK inquiry but said he did not think it made sense to have two inquiries into Omagh on both sides of the Irish border.
He also denied that his government had not done enough to pursue those responsible for Troubles crimes.
"There is no amnesty in the Republic and there never has been an amnesty given in the Republic," he said in clear reference to the UK's contentious legacy laws.
"The gardaí and the Director of Public Prosecutions are independent of government.
"No direction has ever been given to either not to pursue cases that arose from the Troubles and not to prosecute, those are the facts."
"We have mechanisms, we have changed the law in the Republic on a number of occasions to facilitate the provision of information that the Republic may have in respect of certain crimes."
The inquiry will be established under the Inquiries Act 2005 with full powers, including the power to compel the production of documents and to summon witnesses to give evidence on oath.
Lord Turnbull said he was confident the terms of reference would allow him to conduct a "thorough and robust investigation".
He said the voice of the victims would be heard.
"Whilst I have not yet defined the exact procedure the inquiry will follow, it is my intention to invite families and survivors to commemorative hearings in Omagh at some point this year, so I can hear directly from those most affected by the bombing," he said.