Prime Minister Gordon Brown today announced a review of intelligence material from the Omagh bombing after claims in a TV documentary that the bombers' phones were being tapped.
Sir Peter Gibson, the Intelligence Services Commissioner, will examine all intercept material from the security and intelligence services and how it was shared.
A BBC documentary claimed GCHQ was recording the bombers' calls before the 1998 atrocity, which killed 29 people.
The Cabinet Office said the review should be completed within three months.
A spokesman said: "The Prime Minister has invited the Rt Hon Sir Peter Gibson, the Intelligence Services Commissioner, to review the intercepted intelligence material available to the security and intelligence agencies in relation to the Omagh bombing and how it was shared."
Yesterday, victims' relatives warned the Government it faces legal action within a week if it does not hand over intelligence files which could have helped to catch the bombers.
They want to use any transcripts or recollections from individuals relating to mobile phone calls between the bombers on their way to Omagh in their ongoing civil legal case against five men they blame for the tragedy.
The Omagh blast was the worst atrocity of the Northern Ireland conflict. Nobody has been convicted of murder and grieving families are demanding an independent cross-border public inquiry into events before the blast and the security force investigations.
Yesterday, at a meeting in Belfast, victims' spokesman Michael Gallagher demanded action to bring the intelligence services to account.
He said he would be writing to Police Service of Northern Ireland (PSNI) Chief Constable Sir Hugh Orde and the Irish and Spanish governments, whose citizens also died, after the Panorama programme's findings.
Former police ombudsman Nuala O'Loan published a damning critique of the police investigation, accusing detectives of letting down victims and their families.Reuse content