Sinn Fein could take its place on the Northern executive before decommissioning starts under the Belfast Agreement, the Taoiseach said.

But Mr Ahern added that it was not politically realistic to argue that the executive and the North-South council be established without an understanding of how the implementation of the decommissioning part of the agreement would be taken forward.

Replying to a series of questions on the North, the Taoiseach said:

"The agreement does not contain a precondition that there must be a start to decommissioning before Sinn Fein can take its place on the executive. I must be on the record of the House 100 times in saying that over the past 12 months. Such a precondition simply does not exist. "Under the size of its mandate, and under the terms of the agreement, Sinn Fein has a full entitlement to its place on the executive. Both the British and Irish governments have accepted that as the only realistic way forward.

"But the political reality, which I have spelt out in this House, I think since October but certainly since November, is that the UUP interpret the agreement in a different way. Their understanding of the totality of the agreement is that participation by Sinn Fein in the executive does require a start to decommissioning, and the agreement itself provides a mechanism to resolve the decommissioning issue.

"What we have been involved in for months is endeavouring to find a way where we can make the mechanism that is set out in the agreement . . . to find a method within that where we can resolve this matter."

Mr Ahern agreed that he had been "stepping this matter up" in his interview with the Sunday Times. "I have had at least five meetings in recent weeks with Sinn Fein . . . I have always said that decommissioning has to happen and that there can be no place for weapons in a democratic and peaceful Ireland. That is the principle I was reflecting, and I stand by that principle. The issue is one of timing, interpretation, how we get from the present to a point where all the guns are gone. That has to happen as we proceed along the route.

"As I have been saying in interviews, and stepping up the pressure in recent times . . . I have consistently stated my belief that all parties, including Sinn Fein, have to clear their minds on how they would proceed to implement the responsibility under the agreement to make its decommissioning part happen. And in this context, I believe it is not reasonable, nor politically realistic, to argue that the executive and the North-South council be established without an understanding of how the implementation of the decommissioning part of the agreement would be taken forward."

Mr Ahern said that the headline on the article relating to his interview with the Sunday Times, which had been given in all of the news bulletins throughout the North, had implied that Sinn Fein should be barred from the executive unless the IRA first decommissioned. "I never said that, and I never used the word barred. I acknowledge that the journalist admitted this on RTE."

The Taoiseach was replying to the Fine Gael leader, Mr John Bruton, who said he would accept everything which Mr Ahern had said in his interview in the Sunday Times, as published in the Internet. Mr Ahern had said something a bit more explicitly than he had said it in the House, but not in any way inconsistent with it, he added.

Mr Ahern told the Fine Gael spokesman on Northern Ireland, Mr Charles Flanagan, that Mr Martin McGuinness of Sinn Fein had not seen the article in the Sunday Times when he spoke to him on Sunday. "What Mr McGuinness was querying was the headline which he had heard on the radio."

Asked by Mr Bruton if he was to any degree surprised that Mr McGuinness was speaking to him without having first read the article in full, the Taoiseach replied: "Mr McGuinness rang my home . . . there was a call on the answering machine, and I rang him back. But he had also been talking to an official who told me that he was looking for me. So I rang him back. It has been my practice since I became Taoiseach to ring the Northern party leaders - all of them except Dr Paisley - on a regular basis, and particularly at weekends."

Mr Ahern revealed that Mr McGuinness had spoken to himself and to a government official on Sunday. He was asked by the Labour leader, Mr Ruairi Quinn, if Mr McGuinness had offered any indication of what Sinn Fein would see as breaking the political impasse.

Mr Ahern said that he had not had a lengthy conversation with Mr McGuinness, but they had had a number of meetings recently. There had been two meetings last week between government officials and Sinn Fein.

"I have to say that, in my view, Martin McGuinness is genuinely trying to find a resolution of this matter for some considerable time, but with difficulties. It is not an easy position . . . I think that, without breaking a confidence, some of the solutions we have put on these matters are being closely examined by Sinn Fein. But I could not say that any of those have yet seen favour or achieved agreement. There is no formula at this stage; formulae we put forward are being examined."

Earlier, Mr Bruton said that he wanted to wish everybody involved, including the Taoiseach, well in the finalisation of the arrangements for the implementation of the Belfast Agreement. "For that agreement to work, we need to have executive participation by both the Ulster Unionist Party and Sinn Fein, and that is the objective to which all must work."

Mr Caoimhghin O Caolain (SF, Cavan-Monaghan) said that Sinn Fein was fulfilling its obligations regarding all aspects of the agreement and the party continued to work constructively and in good faith with the independent commission on decommissioning.

The plain truth, he added, was that there was absolutely no obstacle in the agreement to the immediate establishment of the executive with Sinn Fein participation. The introduction of the additional baggage of the "ah, but" to that had created great difficulties within the equilibrium of the agreement.