Omagh was the biggest loss of life in a single attack in the Troubles
Prime Minister Gordon Brown has announced a review of intelligence material from the Omagh bomb.
The move follows an investigation by the BBC's Panorama programme.
It revealed that GCHQ was monitoring Real IRA phone conversations as the bombers drove the device into the town in August 1998.
Twenty-nine people and unborn twins were killed in the attack, which was the worst single atrocity of the Troubles, in Northern Ireland.
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."
Extracts from John Ware's Panorama investigation'
The Chief Constable Sir Hugh Orde said the review was a "positive thing".
"I think it's helpful that the prime minister has made an announcement and the allegations in the TV programme will now be looked at," he said.
"We need to wait to see what comes out of that investigation. I have no intention of talking about intelligence, I never have and I never will.
"But I do think it's important that we now step back and wait and see what this inquiry uncovers so we can talk about a shared understanding of what the facts actually are."
On Tuesday families bereaved by the Omagh bomb threatened legal action to try to force the intelligence services to hand over information about the bombing.
The families want access to tape recordings of the conversations and/or transcripts of what was said.
The relatives are currently involved in a civil action against those they believe they were involved in the bombing and want the phone evidence to try to help their case.
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