The Irish prime minister has said he knew a lack of detail over IRA decommissioning would prove problematic for the political process.
Mr Ahern "understood the general's reasons for confidentiality"
Bertie Ahern said a demand for clarity was always going to prove a difficulty.
On Tuesday, Ulster Unionists rejected the IRA's latest act of decommissioning as not being transparent enough.
Talks resumed on Wednesday in an effort to rescue a potential deal to restore devolution in Northern Ireland.
Arms chief General John de Chastelain's report confirmed the quantity of weapons put beyond use by the IRA was "considerably larger" than that which had been previously decommissioned by the republican movement.
Speaking in the Irish parliament on Wednesday, Mr Ahern said he was "deeply disappointed that our efforts failed".
However, while he was very frustrated, he said it was "a new day and we have to get on with it".
Mr Ahern told the Dail that Downing Street was aware that on Tuesday morning he was reluctant to travel to Hillsborough because of concerns about the decommissioning element.
He said he had been trying to get in contact with General de Chastelain since 1830 BST on Monday, but was unable to do so until he met him on Tuesday at Hillsborough.
Mr Ahern said he knew the confidential details over the acts of decommissioning would be problematic.
"I always felt it was going to be a difficulty, for immediately people would say you need more clarity and more details.
"Of course, while General John de Chastelain gave a large amount of details on it... he couldn't say there was 95 of this, or 36 of that or 11 of the other.
"I knew that he couldn't say that and I also knew that had the potential for someone to say that we need to know the exact amount."
Speaking in the Commons on Wednesday, Mr Blair said it was "deeply frustrating and disappointing that we were not able to have the full range of agreements that we thought we were going to be able to achieve yesterday".
However, he added: "I don't think that people should lose sight of the enormous progress which has been made in Northern Ireland over the last few years.
"The truth is, there is an enormous prize to be gained if we can get this last bit of the way."
Northern Ireland Secretary Paul Murphy later told the Commons he had made an order to enable fresh elections to the assembly to take place on 26 November.
Speaking earlier on Wednesday, Ulster Unionist leader David Trimble said he had made it clear to republicans "what would be successful and what would not be successful".
"When we listened to de Chastelain and realised they had imposed restrictions on him, and had not given the information that they knew was necessary, then we knew there was a serious problem," he said.
"That's why I put things on hold."
Speaking at a news conference on Wednesday, Sinn Fein President Gerry Adams said there had been an agreement reached and all parties to the "sequencing" of Tuesday knew what was to take place.
There were now profound difficulties in the process, he said.
It was of key importance that when a commission established under law said it had witnessed IRA decommissioning in accordance with a government scheme, it was up to the two governments to "defend it, promote, validate and uphold it", said the party leader.
"Following our discussions and even our attempts to have dialogue this morning, we still have no satisfactory explanation why the agreed sequences did not go forward," he said.
Mr Blair and Mr Ahern held talks with Mr Adams at Hillsborough later on Tuesday.
The devolved administration at Stormont was suspended a year ago amid allegations of IRA intelligence-gathering in the Stormont government.
The announcement of an election date came after weeks of top-level negotiations between Sinn Fein and the Ulster Unionists, as well as the British and Irish Governments.
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