Ahern and Blair press conferencesThe British Prime Minister said the unionist requirement for what he called "more particularity" about the details of the IRA's latest act of decommissioning had raised new problems.
Mr Tony Blair said "a substantial act of decommissioning" had taken place but he admitted there were problems concerning the detail of the report given by Gen John de Chastelain.
The head of the International Independent Commission on Decommission earlier gave his assessment of the scale of the putting beyond use of IRA weapons.
However he could not give any significant details of what was done as he was hidebound by a confidentially clause with the IRA.
Addressing a press conference last night, Mr Blair, with the Taoiseach, Mr Ahern, said no further attempts at a settlement of the issue would be made last night as it was clear no immediate solution would be found.
Mr Blair added that the Assembly elections would still be held as planned on November 26th, but as things stood, the atmosphere would not be as positive as planned if the latest obstacles were not overcome.
Admitting to frustration, the Prime Minister pointed to the advances made during the course of the day.
"There has been a very clear statement by Sinn Féin this morning, endorsed by the IRA, that all paramilitary activity will cease.
There has been a clear statement that implementation of the Good Friday Agreement is what brings conflict in Northern Ireland to an end. There has been an act of decommissioning certified by the IICD.
"The date for the election has been set and all this is very positive," he said.
The disagreement, he added, was a simple one and centred on the detail of Gen de Chastelain's report. Unionists "need to know the specifics, they need to know what it was and they need to know that in far greater detail than set out in the statement that Gen de Chastelain read out."
Admitting that efforts had come to an end for the evening, Mr Blair said: "It is better that we make sure that the right discussions take place between the parties, which I know is going to happen, and try and get a result over the next few days."
If things were resolved, then the election would take place in a positive climate, Mr Blair said, but if not, then the situation would be more difficult. He said it was frustrating to be in possession of the detail that was sought - but not a position of making it public.
"We shall just have to try, try and try again."
The Prime Minister said he remained "reasonable optimistic" and that he owed it to people to try and work towards a solution. He pointed again to positive aspects of the situation in Northern Ireland.
He noted the economic improvements and the most peaceful climate on the streets for some 30 years.
Mr Ahern said he was sad to have reached such a problem.
The Sinn Féin and IRA statements earlier in the day were "highly significant", he said.
"The clear fact is that the agreement is framework for the full closure of the conflict, exclusively peaceful and democratic moves are the only way to the future."
He said the IRA decommissioning act was "substantial" and he went on to repeat many of the details outlined in the afternoon by Gen de Chastelain.
Referring to the UUP requirement for more details of what arms were put beyond use by the Provisionals and witnessed by the IICD, Mr Ahern said: "Obviously that creates a difficulty," but if the IRA move did not create the confidence necessary among unionists, then he said the parties and the two governments would have to find a way around that.
"It's been a difficulty for some time and it remains a difficulty tonight," he added. "We just have to see if we can find a solution to that. We will just have continue to work hard to find away around it."
He admitted the situation was not simple as it involved rules and legislation, but if the problem took a few more more days, then so be it.
Asked by The Irish Times was it not a nonsense that the process was held up again on the issue of weapons decommissioning, especially on the day when the two governments accepted that paramilitary activity by the IRA was effectively at an end, the Prime Minister returned to the question of confidence.
He stressed that unionist confidence in the process was crucial.
"These are critical issues for parties," he said. "You can't see it from both perspectives and then see how the two can be brought together . . . At one level you could ask 'what does it all matter?' but it does matter."