The Government is warning the republican movement that it must provide "actions as well as words" to reassure Unionists that the IRA ceasefire is permanent.
Tony Blair and John Reid, the Secretary of State for Northern Ireland, will give their joint assessment on the state of the peace process in the Commons on Wednesday in response to a request from David Trimble, leader of the Ulster Unionists.
Mr Blair and Mr Reid will warn that the Government will in future take account of continuing activity by the paramilitaries, such as buying weapons and drawing up "hit lists" of targets, when deciding whether their ceasefires are still holding.
A gradual tightening of the way that ceasefires are measured is seen by ministers as the best sanction available to the Government. If paramilitary groups continue such actions, their ceasefires could be declared over.
The Prime Minister and Mr Reid are expected to give a cautious welcome to the IRA's apology last week for killing civilians. But they will urge republicans to go further. "There is no acceptable level of paramilitary activity on either side," a government source said yesterday. But the Government is expected to stop short of threatening to expel Sinn Fein ministers from Northern Ireland's power-sharing executive.
Yesterday Mr Trimble, Northern Ireland's First Minister, called on Mr Blair to make clear there would be "consequences" if republican paramilitaries did not implement a "clear and unambiguous" ceasefire.
Speaking on the 30th anniversary of "Bloody Friday," when 20 IRA bombs left nine people dead and 130 injured, Mr Trimble said the apology did not reflect the "serious violence" involving the republican movement in Belfast in the past couple of months.
He told the BBC's Breakfast With Frost programme: "What we want to see happen is the peace that we were promised four-and-a-half years ago, and we want to see the paramilitaries carry out the undertakings they gave to have a complete and unequivocal ceasefire. And of course to carry that through with the decommissioning of weapons."
He added: "That's the responsibility of the paramilitaries, and it's the responsibility of the Prime Minister to put pressure on them to do that."
¿ A 19-year-old Protestant was shot in the Ardoyne area of north Belfast yesterday. He was taken to hospital, where his condition was described as "ill but stable". A community representative claimed a nationalist gunman fired a shot across the peace line. Security forces were posted to the area to keep crowds of nationalists and loyalists apart.
On Saturday night, a petrol bomb was thrown into the home of an elderly Protestant man in north Belfast, setting fire to curtains and furniture.
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