The Taoiseach has warned that the political advances made in Northern Ireland will "fall apart" if decommissioning of paramilitary weapons does not take place by next May.
With the Ulster Unionist Party's February deadline for its continued participation in the executive approaching, Mr Ahern declared that the decommissioning issue could not be avoided. "Decommissioning of arms by May 2000 was part of the agreement and that cannot be dodged in any way", he said.
Mr Ahern's prediction - in effect that the executive will collapse within a relatively short time without actual decommissioning - places further pressure on the republican movement in the run-up to next month's crucial Ulster Unionist Council meeting.
Speaking to South Africa's Institute for International Affairs, Mr Ahern appealed to the republican movement to recognise that "old arguments about surrender are no longer relevant". He added: "How can you say an organisation surrenders by decommissioning when you already have two of your senior members inside the cabinet, directing policy?"
While Mr Ahern repeated that the deadline in the Belfast Agreement for decommissioning was May 2000, his comments highlight the Government's concern that the date set by the Ulster Unionist Council for its next meeting could precipitate a much earlier crisis in the peace process.
Mr Ahern's remarks show that he has accepted that the UUC meeting represents the next major obstacle in the process. "Time is short. It's shorter than I'd like. Mr Trimble has made it shorter than we would all like, but I understood why he did that, I accepted that position."
The Taoiseach insisted that the matter had to be dealt with by the International Commission on Decommissioning, chaired by Gen John de Chastelain. "It is not for me or Tony Blair to say how it should be done. Where, when and how it will be done, I don't know, but I do believe this issue has to be addressed."
He said that the leaders of Sinn Fein would have to convince their colleagues in the IRA to decommission, pointing out that he had always maintained that the two organisations were separate, but inextricably linked - "two sides of the same coin".
In Washington, the president of Sinn Fein, Mr Gerry Adams, described his meeting yesterday with President Clinton as "very good". He praised Mr Clinton for having a "strategic viewpoint [which was] ahead of most others on how to make peace work".
Mr Adams said that he had discussed with Mr Clinton the President's view of what needed to be done to "bring about full implementation of the Good Friday agreement - you bring about justice and you make politics work".
In an earlier meeting with White House officials, Mr Adams raised issues such as the implementation of the Patten Commission recommendations, demilitarisation, the Rosemary Nelson and Pat Finucane murders and "other cases of injustice".
Asked about Mr David Trimble's emphasis on the need for IRA decommissioning, Mr Adams said: "I made it clear before I left Ireland that Mr Trimble has to lead his party and be true to the Good Friday agreement . . . Deadlines, ultimatums have not worked anywhere in the world in trying to get peace processes to come to democratic conclusions."
Asked about a statement in the House of Commons by the Northern Ireland Secretary, Mr Peter Mandelson, to the effect that decommissioning could take place by blowing up weapons or making them inaccessible, Mr Adams said that he had not heard these remarks. "Secondly, I have no weapons to blow up", he added.
Meanwhile, the British Prime Minister, Mr Tony Blair, is due to meet Northern Ireland's First Minister, Mr Trimble, in Downing Street this morning to review the political and security situation in the North.
The meeting is expected to be dominated by troop deployment and security arrangements. The future of policing and the decommissioning of weapons are also likely to be discussed.