Speaking at the end of an EU summit in Austria where he assessed the peace deal at a meeting with the UK Prime Minister, Tony Blair, Mr Ahern said: "It clearly is not going to happen."

He told Irish radio that work would continue towards implementing as much as possible of the the agreement reached on Good Friday by the British and Irish governments and Northern Ireland's political leaders.

Mr Ahern called for all parties to work towards the February deadline

On the arms decommissioning issue blocking the peace progress, Mr Ahern added that the agreement should be followed "to the letter of the law".

"What I have been trying to get clear in the past few weeks, and I think I have in meetings with Martin McGuinness (Sinn Fein's chief negotiator), is that it is Sinn Fein's view and policy to continue to make sure that decommissioning happens during the life of the agreement, or in the two-year period set down in it.

"If that happens, they have complied with the regulations."

He added: "Of course I have pointed out the value of it happening earlier, rather than later.

"But they are not incorrect in their view that we have to move on with the other aspects of the agreement."

Decommissioning tension

Mr Ahern's comments follow a warning issued by Mr McGuinness that growing tension over decommissioning was threatening to "poison" the peace process.

He made the warning in response to demands from the Ulster Unionists that the IRA hand over its weapons before Sinn Fein is allowed to take seats in the new Northern Ireland Assembly.

Mr McGuinness acknowledged that the peace deal stated that the assembly executive and a north-south ministerial council should be set up by 31 October without the necessity for disarmament.

Call for completion of agreement

"What we have to try to do is continue with both the Ulster Unionist Party and Sinn Fein, and the other parties, to do the work necessary so that the February deadline (for the transfer of powers to the new Assembly) - which is really the crucial deadline, is not lost."

Mr Ahern noted that "a substantial amount of work" had already been done on the north-south bodies, and added: "We have to try to continue to complete it."

He said he believed that if the agreement continued to be implemented in all its aspects, both republicans and loyalists would become more confident.

"What Tony Blair and I are committing ourselves to do, even though there are some risks and some chances, is to continue to move along."

Mr Ahern said a suggestion by former Irish cabinet minister Dr Conor Cruise O'Brien that unionists should seek a deal for inclusion in a united Ireland was "different".

However, the Irish Prime Minister added: "If the argument is that constitutional nationalists and constitutional unionists should work closer together, that is always to be welcomed."

Robert McCartney, leader of the UK Unionist Party, maintained on Irish radio the O'Brien plan, spelled out in the ex-minister's memoirs, did not contain anything new.