The Rev Ian Paisley's Democratic Unionist Party (DUP) will boycott next week's review of the Good Friday Agreement, while the Ulster Unionists, led by David Trimble, announced they would not hold direct talks with Sinn Fein.
Mr Paisley said the review would try to achieve "some sort of fudge on the decommissioning of illegal terrorist weapons". He added: "The DUP has not been, and will not be, part of a process designed to facilitate the entry of Sinn Fein/IRA into the government of Northern Ireland and to advance the republican agenda of the Belfast [Good Friday] Agreement."
Mr Paisley said it was time Mr Trimble's party "came to its senses and freed itself from a process which is dragging Ulster further down with every passing day".
Yesterday Mr Trimble suggested his party would take part in the review, provided that the behaviour of the paramilitary groups in the province was the "key issue".
The Ulster Unionists said that the talks should centre on whether terrorists were truly committed to ending violence: "This is the essential prerequisite for success and will determine our subsequent engagement in the review."
The party will not totally boycott the review but has ruled out face- to-face meetings with Sinn Fein, insisting: "Dialogue can only be conducted with those who are genuinely committed to exclusively peaceful means."
John Taylor, deputy leader of the Ulster Unionists, insisted a final decision would be taken today by the party's 100-strong executive, but said: "I will not personally be involved in any bilateral meetings with Sinn Fein/IRA while it pursues a policy of targeting, attacking and expelling people from this province."
Sinn Fein condemned the Ulster Unionists' announcement and accused the party of engaging in the "old exclusivist politics which have proven to be a total failure and disaster in the past".
In an interview with London Weekend Television to be broadcast today, the former American senator George Mitchell, who will chair the review, insisted a deal could be reached. He said: "It is unthinkable to me that, after having reached agreement, the parties who support the agreement will permit it to fail. That would be a terrible tragedy, an irony and I think it would be unforgivable."
He said: "History might have forgiven the failure to reach an agreement since few thought it possible. History will never forgive the failure to implement an agreement once reached."Reuse content