Northern Ireland's police ombudsman has announced that she is to probe claims that security forces were given 48-hours warning of the Omagh bombing.

Nuala O'Loan is to hold an inquiry into the claims of an RUC double agent who says he tipped off his handler that a bomb was being made by a well-known dissident republican paramilitary.

The agent, known as Kevin Fulton, believes the worst terrorist atrocity in Northern Ireland's history could have been prevented if the information he handed over had been acted on immediately.

Fulton maintains he gave security sources a "head start" which should have been exploited to prevent the blast which killed 29 people on a crowded shopping street three years ago.

The decision to investigate the claim is being made on the grounds of public interest.

Senior security officials vehemently deny they had prior warning about the Real IRA's activities in the days leading up to the Omagh bombing.

In a statement issued on Thursday the RUC said it hoped the investigation would disprove Fulton's claims.

"The chief constable has discussed the matter with the ombudsman and welcomes her examination of the issue which he hopes will be reassuring to the families of the victims of this dreadful atrocity," the statement said.

Whilst Fulton is maintaining that he did blow the whistle on the Real IRA's bomb-making activities, he denies that he knew of the exact timing or location of the bomb.

His lawyer, Imran Khan, said on Friday: "What is clear is that he is not saying that he knew the Omagh bomb was going to go off but information wasn't passed on which could have given the RUC a head start in relation to finding out what precisely was happening."

Victims of those killed have welcomed the announcement. Michael Gallagher, who lost his son Adrian in the bombing, said: "I think that the office of the Ombudsman is the proper people to investigate these allegations. I would like to see them investigate it as thoroughly and as quickly as possible."