The Irish-British proposals to restore the power sharing assembly are the best the two governments can do and the Northern political parties have just days to decide whether to accept them, the Taoiseach, Mr Ahern said after a morning of negotiations.
Following lengthy talks in Downing Street with Prime Minister Tony Blair, Mr Ahern told journalists: "Two years on from the institutions collapsing, a year on from the election, three gallant efforts by everybody to reach a conclusion, you have to call it, and we have to call it within a matter of days."
Sinn Fein leader Gerry Adams, with Mitchel McLaughlin, right, Michelle Gildgernew and Martin McGuines as they arrive for a meeting the Taoiseach at the Irish embassy in London today.
Mr Ahern said tonight he was confident the Rev Ian Paisley was sincere about striking a deal with republicans.
He said he could understand the rationale behind the Democratic Unionists' insistence that IRA decommissioning is photographed but stressed the proposals were not designed to embarrass anyone.
"I have no doubt that Dr Paisley is of the mind that if the circumstances are right, and if the clarifications of the issues lead to acts of completion, that he wants to move ahead," he said.
Mr Ahern said the governments had received from Sinn Fein and the Democratic Unionist Party (DUP) comprehensive lists of points on which they wanted clarification.
The two governments would seek to provide that clarification over the next couple of days. The governments would then expect a prompt response to the proposals from both sides, he said.
Devolved government could be back in Northern Ireland by next spring if a deal involving Sinn Féin and the Democratic Unionists is struck within days, sources close to the talks said.
DUP sources said the British and Irish Governments would try to roll out a deal to get power sharing back by next March.
However they added a lot would depend on whether the IRA was prepared to become an "old boys association" as DUP leader, the Reverend Ian Paisley, suggested.
A party source said: "The talks at this stage are inching forward but I am not in a position where I can say that a deal will definitely happen.
"I think we are all coming to the point where the parties will soon have to make a judgment about what's on offer but right now the ball is in the court of the two governments.
If the parties refuse to sign up, both the Taoiseach and the Prime Minister are ready to publish the proposals.
Both leaders held a series of meetings with the DUP and Sinn Fein negotiating teams in London this morning looking for a response to Irish-British proposals submitted to the parties last week.
The Taoiseach also met DUP leader the Rev Ian Paisley who had strongly suggested that the latest deadline of tomorrow for progress would not be met.
"I don't want to put in to the minds of people that we have gone from A to Z. We have not. But there has been progress," Rev Paisley added.
After meeting with Mr Ahern, Rev Paisley said straight talking had taken place and he suggested that the IRA should become an "old boys' association".
He again insisted the group must complete decommissioning of its arms and turn its back on "criminality" but appeared to concede the organisation could remain in some form.
Rev Paisley said he was also awaiting a paragraph by paragraph response to the points he had raised from Mr Blair.
Mr Ahern described the meetings with the political parties as useful but added that there remained work to be done. With no clear timeline for an agreement in sight Mr Ahern backed away from tomorrow's deadline and reiterated that time was short.
British and Irish officials hope their formula for reviving the Stormont Assembly and removing the gun for ever from Northern Ireland politics will succeed.
A Sinn Fein source said: "The DUP's response at today's meetings in London could be critical. "We could get a real sense today if this is going to float."
A DUP source said progress was being made. "There has been a narrowing of the gaps but at this stage I would still be a little cautious about making any predictions," he said.
The British and Irish governments are also facing demands that they bolster any deal reviving power sharing with a special fund to help devolved ministers make a real difference on the ground.