Relatives of the Omagh bomb victims are launching legal action in a bid to force the British and Irish Governments into granting a full scale cross-border inquiry into the atrocity.
They are planning High Court applications in Belfast and Dublin seeking leave to apply for a judicial review.
The announcement followed a meeting on Monday with the Northern Ireland Secretary of State Theresa Villiers.
Outside Hillsborough Castle, Co Down, Michael Gallagher - whose son Aiden was killed in the attack - said: “We’re tired of waiting for a decision. We could go on like this for the next 10, 20 years. We`ve been left with no choice but to go down the legal route.”
Talks have been arranged with legal representatives tomorrow in advance of the applications being lodged.
Last summer copies of a confidential report - specially commissioned by the families to review all the various police investigations - were handed over to the Republic’s Justice Minister Alan Shatter and the then Northern Ireland Secretary Owen Paterson.
The Omagh families have been pushing for a full cross-border tribunal of investigation following the acquittal in December 2007 of Sean Hoey, an electrician from Jonesborough, south Armagh, the only man to stand trial for the murders.
No details of the report were released, but it is understood the 60 page document claims significant security failings before, during and after the bomb exploded in Omagh’s Market Street in August 1998, killing 29 people, including a mother pregnant with twins.
It alleges that the RUC, Garda, MI5 and the FBI failed to share important intelligence.
The report also claims the discovery of e-mail evidence detailing certain terrorist activity in the Republic but which was not shared with the authorities on the northern side of the border. It is believed to be linked to claims of two separate bomb attacks in Northern Ireland which were allegedly allowed to go ahead undetected in order to protect the identity of an informer.
Mr Gallagher who spent over an hour with Ms Villiers, claimed she told them she had “significant insight” of the issues involved, but further discussions, including talks with the Irish Government were necessary.
There was no indication from her of support for the cross-border inquiry, he said.
Mr Gallagher said: “We were able to articulate to the Secretary of State the grave issues of concern that are contained in the report.
“We acknowledged that many issues are likely to embarrass both governments. The public interest in knowing the truth of what occurred prior to, at the time of and beyond the Omagh bomb is of greater need.”
An NIO spokesperson said the Secretary of State was still considering whether it would be in the public interest to hold an inquiry.
She added: “Her meeting with representatives of OSSHG (Omagh Support and Self Help Group) this morning was part of the thorough process she has undertaken to assist in making this decision.
“The Secretary of State advised the OSSHG that she hopes to make her decision very soon, once she has consulted all those with an interest.”