An RUC spokesman confirmed that "two people are now helping police with their inquiries into the bombing".

The remains of the car containing the Omagh bomb.

Seventy-eight victims of the car bomb, which killed 28 people, are still in hospitals throughout Northern Ireland.

Seven of them are in a critical condition.

Police have traced the final movements of the car which contained the bomb. They said two men were seen getting out of the maroon Vauxhall Cavalier in Market Street at least 40 minutes before the explosion.

The UK Prime Minister Tony Blair, having welcomed the Irish Government's decision to strengthen its anti-terrorist laws, has said his government will follow suit with similar measures.

Tories offer support for new laws

Blair: Pledged to introduce new security measures to match those passed by the Irish government

Northern Ireland minister Paul Murphy said the government "was looking very carefully" at legal implications of how to implement any new laws.

The deputy leader of the Conservative Party, Peter Lilley, said the government could count on Opposition support for the move.

But Sinn Fein's chief negotiator, Martin McGuinness, said emergency legislation had not succeeded in the past.

"I think a much more important weapon is the power of people, particularly those people within republicanism, in overwhelming numbers, who have supported the strategy of people like Gerry Adams and myself," he said.

Civil rights concerns

Others have also raised concerns about the possible threat to civil liberties.

Corbyn: No need for new laws

Left-wing Labour MP Jeremy Corbyn warned that new laws promised by Tony Blair were not only unnecessary but could also prove counterproductive.

"It could create further miscarriages of justice and it could create further martyrs. We need to continue with the peace process and defeat these people politically," he said.

Civil rights organisations in the UK and Ireland voiced similar fears.

Paul Mageean, from the Belfast-based civil rights group the Committee for the Administration of Justice - which was awarded the Council of Europe human rights prize - warned that the UK government could not proceed to introduce the new measures without first debating them at Westminster.

"I don't think you could change the law in the way they seem to be proposing without a recall of parliament," he said.

Miscarriages of justice fear

Mr Mageean said the evidence of previous security clampdowns suggested the main effect could be to convict and imprison innocent people - such as had happened to the Birmingham Six and Guildford Four, all of whom were later found to be victims of miscarriages of justice.

Rory Mungoven, of the human rights group Amnesty International, criticised the government's plan to make it easier to secure convictions for belonging to proscribed organisations.