The leading dissident Ulster Unionist MP, Mr Willie Ross, has voiced his "total opposition" to his party leader meeting Mr Gerry Adams for their first one-to-one talks on Thursday.
Mr David Trimble yesterday met the Sinn Fein president and other party leaders at Stormont Castle in Belfast. The UK Unionists and the DUP boycotted the event. Mr Trimble will hold bilateral discussions with Mr Adams on Thursday in his role as the North's First Minister.
However, Mr Ross said: "We should not be talking to Sinn Fein/IRA in the absence of decommissioning and the disbandment of their terrorist organisation. Just because our party leadership has shifted position on this one it doesn't mean the membership has shifted too."
Mr Ross said he believed he had the support of many prominent dissidents in the party. Other anti-Agreement UUP sources said divisions in the party were growing.
Yesterday's meeting lasted just over an hour and was described as "workmanlike" by Mr Trimble. It was called to plan the future of the North's new power-sharing administration. Decommissioning was not mentioned during the meeting, according to Mr Adams, but it clearly provided the one difficult moment.
In a brief statement, Mr Trimble said: "The only point of contention was when Sinn Fein representatives raised the question of the formation of the shadow executive. We pointed out that under the Agreement a number of things must happen. That there must be progress on a number of things, that there must be progress on all matters and this puts a particular responsibility on paramilitary-related parties."
Mr Adams said it had been a positive engagement. "The meeting was conducted in a good atmosphere and there was no acrimony." He said Sinn Fein had been treated equally with the other parties. When asked if his party had talked directly to Mr Trimble, he said: "There was direct face-to-face engagement between everyone in the room." Mr Adams said Sinn Fein would address the decommissioning issue in good faith but insisted there was an "automatic right" of every party which received a mandate at the election to play a full part in all the structures of the Assembly.
The meeting focused on the numbers and make-up of ministerial portfolios and the timeframe for the establishment of the executive and cross-Border bodies as well as the other elements of the Belfast Agreement.
No decisions were made, but private meetings between Mr Trimble and the parties will take place this week in order to reach a consensus to put to the Assembly when it reconvenes on Monday.
The North's Deputy First Minister, Mr Seamus Mallon, said problems existed but could be resolved by dialogue. "I believe it can be done and it will be done, and there is no reason it will not be done quickly," he said.
Although the DUP did not attend the meeting, its party leader was at Stormont. Dr Ian Paisley said he would never sit down in government with Sinn Fein. But he insisted his party would take the two executive ministerial posts to which it was entitled.
Dr Paisley said: "We are not negotiating the future of our province with them [Sinn Fein], nor are we taking part in any acts of government with them."