Anti-agreement unionists were destroying their link with the Union by opposing the institutions of the agreement, Mr Martin Mansergh, adviser to the Taoiseach, has said.
This was because the collapse of the institutions would be detrimental to the Northern Ireland economy, he added.
Mr Mansergh was speaking last night at the opening of a conference in University College Cork, entitled "Northern Ireland: Paths towards Peace".
"I personally am amazed that the anti-agreement factions cannot see they are vigorously sawing off one of the branches on which the Union is sitting. Preventing the Northern Ireland economy from maintaining its competitiveness, not least with the Southern economy, will do nothing for the long-term future of the Union," Mr Mansergh said.
He said the buoyant state of the Republic's economy had made increased North-South co-operation of more interest to unionists.
Other speakers at the conference, continuing today, include former Taoiseach Dr Garret FitzGerald, Ms Kathy O'Toole, a member of the Patten Commission, and Fintan O'Toole, an Irish Times columnist.
Police reform in Northern Ireland was important for continued constitutional and democratic politics. An acceptable police force supported by all communities was vital for stability, he added.
"With all due allowance for difficulties of transition, constitutional and democratic politics is not compatible in the long run with the maintenance of private armies, which will simply store up trouble for the future. Police reform is relevant to that."
Mr Mansergh added the Belfast Agreement would probably not have happened without the provision for the release of prisoners.
"Nevertheless, the release of prisoners has been deeply disturbing to the unionist community in particular, especially the triumphalism displayed at the special Sinn Fein Ardfheis, and much more recently the gun-toting antics of some loyalists." He said he believed the Remembrance Day bomb in Enniskillen was the catalyst for the peace process. Dialogue with the IRA opened up debate.
"The ideological issues underlying conflict were for the first time being directly addressed and debated, such issues as whether Britain still had a strategic interest in Ireland or was politically neutral, the divisive and weakening effect of armed struggle on nationalism, and the conditions under which Irish unity could be achieved in future."