The Ulster Unionists have failed to agree on whether they will take part in next week's review of the implementation of the Belfast Agreement to be chaired by Senator George Mitchell.
The party has also delayed a decision on initiating a legal challenge to Dr Mo Mowlam's ruling last week that the Provisional IRA ceasefire had not been broken.
The UUP Assembly party met at Stormont yesterday. The party's deputy leader, Mr John Taylor, said he could not recommend that the UUP take part in the review while the Provisional IRA continued to kill and expel people.
"I do not believe we should be participating with Sinn Fein in the review under the present circumstances. You cannot have, as we do, a party participating in the democratic process while the organisation behind it is sending Ro man Catholics out of the country or, in some cases, killing them."
Mr Taylor and fellow MP, Mr Willie Ross, do not support further contact with Sinn Fein. Mr Ross said last night: "We can't continue with this charade any longer. Not only has the Provisional IRA no intention of decommissioning, but it is continuing to kill and maim.
"Our party leadership made a fundamental mistake in signing up to the agreement. Now is the time for a damage-limitation exercise. We cannot continue to be involved with Sinn Fein."
The Ulster Unionists will hold further meetings to discuss their strategy later this week. After meeting his Assembly party, Mr Trimble said republicans had to prove they had embraced exclusively peaceful means before the process could move forward.
"The question that now must be asked in view of the behaviour of the mainstream republican movement is, `Is it committed to peace and democracy?' Unless we can get this preliminary question settled satisfactorily, what is the point of getting involved in a detailed discussion which is not going to end satisfactorily?"
Mr Trimble said the UUP was still taking advice on whether to mount a legal challenge to Dr Mowlam's statement, but he said the Assembly party was unanimous that the Provisionals had broken their ceasefire and the British government had made the wrong decision in not halting the early release of prisoners.
He condemned all recent violence, including loyalist attacks on Catholic homes in Larne, Co Antrim, but said the discovery of a US gun-smuggling plot was particularly disturbing. "Here we have clear evidence that the IRA are rearming, rearming for what?
Although Sinn Fein has yet to declare if it will take part in Mr Mitchell's review, the party's chief whip, Mr Alex Maskey, said its postponement would damage the peace process. "The main concern people have had in the past 16 or 17 months is that we are continuing to lose very valuable time.
"The momentum is going completely out of the Good Friday agreement and indeed, many people now are questioning its entire credibility. So the notion of deferral of the review would be a serious matter and would further erode confidence in the peace process."
Mr Ian Paisley jnr of the DUP criticised the Ulster Unionists for not immediately ending contact with Sinn Fein. "What is there left to decide? It is evident the ceasefire has broken down."
The SDLP, Alliance Party and Progressive Unionists also warned against the review being postponed. An SDLP spokesman said parties with paramilitary connections must fulfil their obligations by calling for an end to human rights abuses.
"As we enter next week's review, the opportunity to resolve these problems must be grasped. The peace process has been strained almost to the limit by these incidents, but we simply cannot allow them to blow us off course," he said.
The Alliance leader, Mr Sean Neeson, said: "I'm disappointed the Ulster Unionists are engaging in delaying tactics. The important thing is that the review goes ahead as planned."
The Progressive Unionist Party's chief spokesman, Mr David Ervine, said: "George Mitchell is the last chance, certainly for our generation to do something sensible for the benefit of our kids. George Mitchell is standing behind the bar of the last chance saloon and it really is our last opportunity."