The Taoiseach, speaking in the Dáil, stood by last week's proposal from the Irish and British governments that IRA decommissioning should be photographed.
"It was our understanding that this proposal would be considered by them. They have, of course, since said that they are unable to agree to it.
"I believe that the governments' proposals in this respect continue to represent a fair and reasonable judgment and should - in the context of an overall comprehensive agreement - have sufficient to close the gap on this most sensitive issue," he said.
In the Seanad later, he departed from a prepared script to emphasise that the release of the killers of Det Garda Jerry McCabe had to be part of a final deal.
People could not say that they were in favour of such a deal and yet oppose the release: "If you take that view there will never be decommissioning," he told senators.
The leader of Fine Gael, Mr Enda Kenny, sharply criticised the Government for its failure to keep the Opposition informed of Northern developments.
He was briefed on Tuesday by officials from the Department of the Taoiseach and the Department of Foreign Affairs in advance of yesterday's debate.
"Until yesterday, I had received no briefing on Northern Ireland issues for over 14 months. When I received briefings during 2003, the Taoiseach's plan to release these common criminals was never once mentioned," he declared.
"The Government must note that we will take no lectures on bipartisanship from Fianna Fáil, which did everything possible to undermine the historic Anglo-Irish Agreement."
The Taoiseach, he said, could depend on Fine Gael's continued support on the North, but "it cannot ask us to write a blank cheque or expect retrospective approval for secret deals".
Meanwhile, the leader of the Labour Party, Mr Pat Rabbitte, defended Mr Kenny against Government criticism after he questioned Mr Ahern last week over the McCabe killers.
"Such accusations amount to no more than attempted political blackmail. They are an attempt, in effect, to prevent the Opposition doing the job it is required to do in a democracy.
"Despite such attempted political blackmail, whether it comes from the Government or the leadership of Sinn Féin we will continue to do our job. This is our country too," he said.
