The Democratic Unionist Party (DUP) has accused Mr David Trimble of letting the IRA "off the hook" over decommissioning, following the Ulster Unionist Council's endorsement of the First Minister's six-point plan.
The DUP deputy leader, Mr Peter Robinson, claimed the outcome of the UUC meeting demonstrated that unionist support for the Belfast Agreement did not exist.
He said Mr Trimble's support within the UUP was "wafer-thin" and described him as a "minority leader of unionism".
"The basis upon which the Belfast Agreement is constructed calls for cross-community support. Why does the government put the community through this periodic torture instead of attempting to provide an agreement capable of enjoying both nationalist and unionist support?"
Mr Robinson said Mr Trimble had accepted the anti-agreement principle that Sinn Fein should be excluded from governmental institutions until the IRA met decommissioning requirements. However, he said the UUP leader had applied that principle in a "meaningless fashion" to the North-South Ministerial Council.
"If it was right to do it for North-South meetings, why not do it with the Executive itself? What is the argument for not maximising the pressure - hitting them where it hurts - by putting them out of the Executive?" he said.
"Republicans have murdered and taken part in gunrunning over recent times, yet their representatives are permitted by David Trimble to remain in charge of government departments and stay on the Executive.
"If murder and gunrunning are not reasons to exclude Sinn Fein/ IRA, what would be?"
Mr Robinson claimed the UUP was motivated to address issues such as police reform and decommissioning because of a fall-off in its electoral support. Mr Sammy Wilson, DUP Assembly member for East Belfast, said Mr Trimble had gained a "hollow victory" on Saturday. His "day of reckoning with the electorate is coming and even today's shabby compromise will not save him."
Mr Wilson said the UUP leader had no intention of implementing his six-point plan but was merely attempting to gain time with the electorate until his party reviewed the situation in January.
"No one should be fooled by what Trimble has promised," he said. It would be yet another promise for him to break. "He has now set four deadlines for IRA/Sinn Fein to hand in their guns and has broken all four of them."
Mr Wilson said he had heard Mr Trimble praise North-South institutions as recently as last week.
"Why should anyone have trust in his promise to bring those very institutions down by excluding IRA/Sinn Fein? Indeed since he has recently praised IRA/Sinn Fein Ministers, who can possibly believe his synthetic criticism of them?"
"David Trimble's victory could be more accurately described as his Waterloo. It has only been obtained at the expense of a compromise, which is bound to come back to haunt him," he said.
