Northern Ireland Police Ombudsman Ms Nuala O'Loan met the Minister for Foreign Affairs Mr Brian Cowen over claims that crucial information which could have helped catch the Omagh bombers was withheld by the gardaí, it was revealed tonight.
During talks in Dublin, which also involved her executive director Mr Dave Wood, she alerted Mr Cowen of the allegations.
It has been claimed that information supplied by an informant to the Special Branch and which if acted upon, might have thwarted the terrorists, was never passed to the RUC.
Representatives of some of the Omagh families are to meet British Home Secretary Mr David Blunkett in London tomorrow alleging there was little north-south police cooperation in the hunt for the Real IRA terrorists.
Mr Michael Gallagher, whose son Aidan was among those killed, said tonight: "The British and Irish governments lead us to believe there was unprecedented cooperation. But it was only a myth.
"It didn't exist, and we have the evidence to prove it."
It has been alleged that a number of days before the Omagh bombing, an informant told his handler, an officer based in Dublin, that republican dissidents who had asked him steal a car, told him they no longer wanted a vehicle because they had already obtained one.
The information was passed on to the Special Branch but, it is claimed, never reached the RUC - even though the informant had stolen cars previously which were used in terrorist operations by republicans opposed to the peace process.
Ms O'Loan's office tonight confirmed the matter was raised when she met with Mr Cowen after a permanent secretary at the Northern Ireland Office was informed in advance of her departure to Dublin last week.
There was no detailed discussion about the claims, a spokesman added.
Mr Wood, who was with her, is a commander with the London Metropolitan Police and headed an inquiry which produced a highly critical report of the Omagh investigation.
A statement issued in Belfast tonight said: "The office of the Police Ombudsman was introduced by some of those bereaved by the Omagh bomb, to a Garda officer who claimed to have new information about events leading up to, and after the atrocity.
"We examined the information made available to us and satisfied ourselves that it did not contain matters to suggest alleged misconduct by the PSNI/RUC officers. We will not, therefore, be launching any investigation as a result of the information.
"As the material related to matters in the Republic of Ireland, the police Ombudsman's office has now passed the information to the Department of Foreign Affairs in Dublin.
"It has also provided a copy of the material to the police service of Northern Ireland."
The Minister for Justice Mr John O'Donoghue tonight faced calls to explain why the force apparently "withheld information".
Mr Alan Shatter, Fine Gael’s justice spokesman, said: "John O'Donoghue must explain why the Garda Siochana withheld information available to it from the RUC, which may have prevented the Omagh bombing atrocity.
"He should detail the nature of the information that was available to the Garda and when it was received.
"It is the responsibility of the Minister for Justice to ensure that at all times the Garda Siochana competently undertakes its security duties and that they have at all times maintained full communication with the RUC, and its successor the PSNI, to protect the lives of all who reside on this island."
He added: "In light of the statement issued by the Northern Ireland Police Ombudsman this evening, the minister has very grave questions to answer."