The UK Unionist leader, Mr Bob McCartney, has said he will not support Mr David Trimble's appointment as First Minister when the Assembly meets today unless Mr Trimble gives a "complete" assurance he will not enter government with Sinn Fein until the IRA decommissions.
Mr McCartney said decommissioning had to be "substantial". The Ulster Unionist leader had been contradictory in his attitude to allowing Sinn Fein into government and must clarify his position before unionist Assembly members could vote for him.
The First Minister and deputy First Minister are elected together in one vote. Mr McCartney said he would also be asking the most likely candidate for the latter post, the SDLP leader Mr John Hume, to state his position on decommissioning.
Mr McCartney said Mr Hume had already stated he believed Sinn Fein should be allowed into the executive without an IRA arms handover and if this was still his position, he did not see how any unionist could vote for him and Mr Trimble.
The UK Unionist leader also demanded Mr Tony Blair should honour his pledges made during the referendum campaign. "The Prime Minister must clarify and reiterate his answers to the leader of the opposition, William Hague, when he said that no prisoners would be released until substantial decommissioning had taken place.
"Also, the Prime Minister should make it clear whether or not the representatives of armed terrorists will be allowed to take their seats in government without substantial decommissioning taking place."
Mr McCartney claimed democratic and accountable government was being offered to the North only on the precondition of the acceptance of all-Ireland bodies with executive powers and the demise of the Union.