The Ulster Unionist Party has announced it will not be participating in today's multi-party talks at Stormont on the implementation of the Belfast Agreement.
The news means the week-long round of talks - which will include meetings involving the Taoiseach, Mr Ahern and British Prime Minister Mr Tony Blair - will now have no unionist representation.
In a letter to Northern Ireland Secretary Mr Paul Murphy, UUP leader Mr David Trimble argued the discussion of "secondary issues" in today's talks would serve as a "smokescreen to divert attention from the key issue of paramilitarism".
Mr Trimble also objected to the presence of the Republic's Minister of State at the Department of Foreign Affairs, Mr Tom Kitt, at a meeting on matters relating solely to Northern Ireland.
"We cannot, on that ground alone, contemplate participation this afternoon."
The SDLP, Sinn Féin, the cross-community Alliance Party and the Women's Coalition are expected to attend the implementation group talks.
The Progressive Unionist Party (PUP), which is linked to the loyalist Ulster Volunteer Force, has said it will not attend after claiming it was excluded from earlier talks.
The Rev Ian Paisley's Democratic Unionists have refused to play any part in implementing the Agreement and have called for its renegotiation.
