The North's First Minister, Mr David Trimble, has welcomed the joint statement on the peace process from President Clinton, the British Prime Minister, Mr Tony Blair, and the Taoiseach, Mr Ahern.
"The support they have given to the political leaders of Northern Ireland has been essential in maintaining momentum in the process," he said yesterday.
Returning from Washington to prepare for the annual general meeting of the Ulster Unionist Council, he said decommissioning would happen "because the paramilitaries now know it has to happen".
In his address to more than 800 members of the party's grassroots today, Mr Trimble will say it is not a question of whether, but when, decommissioning will take place.
According to UUP sources, his speech will focus on the future challenges and opportunities associated with the devolution of power from Westminster. Education, the economy, agriculture and the reform of non-governmental structures will all be addressed.
Mr Trimble will urge the party to remain united, stressing that anti-agreement unionists offer no constructive alternative. The gains made by unionism abroad and its winning of international respect will be highlighted in his speech.
The Sinn Fein Assembly member for North Belfast, Mr Gerry Kelly, has also welcomed the call by the US, British and Irish leaders for progress in implementing the Belfast Agreement.
He said Gen John de Chastelain was the appropriate person to deal with disarmament. He also welcomed the statement's acknowledgement that some issues had yet to be resolved. "The agreement was a contract between opponents. It was not an agreement between friends," he said. "It was written in very specific terms for that. That is why we argue so heavily for the implementation of the letter of the agreement."
To demand defeat of the IRA, with arms decommissioning, after 30 years of attempting to defeat them in the war situation was not the way to advance the process, he added.