The reintroduction of internment was not being ruled out following calls by the Ulster Unionists for members of the breakaway group to be arrested without charge. But Bertie Ahern, the Irish Prime Minister, gave a clear signal that the two governments believe "other measures" could prove more effective.
The chief constables of the Royal Ulster Constabulary and the Garda are to report to the two governments on what security action is needed across the border, and new measures were promised within the next few days, if they are felt necessary.
Tony Blair last night sought to prevent Unionists and loyalists from hitting back and destroying the peace - attempting to unite all shades of political opinion against the renegade group in a round of meetings at Stormont with political leaders after cutting short his holiday in France.
His official spokesman said the terrorists would be given no hiding place amid rising hopes that they will be "shopped" to the police or the official IRA by their own community.
Unprecedented condemnation of the bombing by the Sinn Fein leaders, Gerry Adams and Martin McGuinness, was seen by Downing Street as a significant break with the past.
"The change in the political situation should not be overlooked," said the Prime Minister's official spokesman. "Overseas or at home, these people have got no friends in high places in any civilised country on earth. They have got no votes, no political support, no great numerical support. They stand for absolutely nothing but terror. They are basically criminals and in some cases psychopaths."
Mr McGuinness hinted the nationalist community will come out against the renegade group, raising hopes that they will be identified. He said: "I think people will make it crystal clear that these people should not be allowed to wreck the peace process."
A special Irish cabinet meeting on Wednesday will decide on measures to strengthen security and surveillance operations.
After chairing an emergency meeting of the Irish cabinet security committee, at which the latest intelligence reports were studied, Mr Ahern pledged "whatever resources are necessary" to deal with the new threat.
He said he believed the republican hero Bobby Sands "wouldn't have stood over the horrific events of yesterday" - seen as a pointed reference to the sister of the dead hunger striker who has founded a dissident republican pressure group. The bombing increased speculation that the split in the IRA could lead to a new and bloody feud.
Andrew Mackay, the Tory spokesman on Northern Ireland, said he believed the lives of Sinn Fein leaders could be at risk. Calling for the IRA to inform on the breakaway group which carried out the bombing, Mr Mackay said: "Adams and McGuinness could be quite worried for their own safety.
"If you look at Irish history, when there are splits in the republican movement, they `do in' the leaders of the mainstream group. I would make sure the security forces get these people first.
"I believe there is an opportunity here for the mainstream republican Sinn Fein-IRA to end the cancer of terrorism in Northern Ireland by cooperating because they know who these people are. "They know the terrorist underworld. If their words mean anything, they must be matched by actions. They should help to arrest these people and wipe out the rest."
Words Of Condemnation
"It is impossible to contemplate, to get in the mind of anyone who could do this ... We will not let these people wreck the future. "
"No stone will be left unturned until we bring these people to justice."
Ronnie Flanagan, Chief Constable of the RUC
"This appalling act ... is designed to wreck the process and everyone should work to ensure the peace process continues."
Martin McGuinness, Sinn Fein chief negotiator
"I have as much respect for the British Government as I have for the IRA. They both of them have played this game of telling people we can win this by concession after concession after concession."
Ian Paisley, Democratic Unionist Party leader
"Once again, blind violence is attempting to impede the difficult path of peace and productive harmony ... my earnest hope ... is that the Irish people of goodwill will not succumb to violence and that they will persevere."
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