The Taoiseach and the British Prime Minister have given the peace process four days to reach a breakthrough.
Mr Ahern, speaking at a celebration to mark his 10th anniversary as leader of Fianna Fail, said ongoing negotiations had been an "exhaustive effort" but that the work was now done and decisions had to be made by the parties involved.
"Tony Blair and myself have to call it, to be precise, in four days", he said.
Sinn Fein president, Mr Gerry Adams, and DUP leader the Reverend Ian Paisley have been engaged in intense talks in recent days as the bid to restore power-sharing institutions in the North moved towards an historic breakthrough.
Earlier tonight, Mr Paisley said he was prepared to do a deal with Republicans provided they "cease to be terrorists". Mr Paisley, speaking after a meeting with Chief Constable Hugh Orde at police headquarters, said the onus was not on his party to decide whether to accept the latest plans from the two governments to restore devolution.
He is under pressure to make a definitive response when he meets British Prime Minister Tony Blair at Downing Street on Monday.
But he said it was up to Sinn Féin to decide whether they would accept the proposals put forward by the two governments.
"This is not negotiations with Sinn Fein. It's an ultimatum to Sinn Fein. Are you going to continue to be terrorists or are you going to quit your terrorist path," he said.
Mr Paisley spoke of his difficulty at coming to an agreement to share power with Sinn Fein. Earlier this week, Sinn Fein president, Mr Gerry Adams, complained bitterly when the DUP leader said the IRA would have to wear "sack cloth and ashes" to atone for a 30-year paramilitary campaign by the IRA.
Mr Paisley said: "I will have to do a good deal of swallowing. I will have to do a good deal of biting my lip in future days. But I'm prepared to do that provided they cease to be terrorists."
Sinn Fein vice president Mr Pat Doherty said the process of negotiation could not last forever. The West Tyrone MP said: "Despite our obvious scepticism about the DUP's approach, and particularly our scepticism about their willingness to buy into the core principles of the Good Friday Agreement, Sinn Fein approached all of these discussions positively.
"We have spent months in detailed and thorough-going discussions with the two governments across all of the issues. I think we have all been patient over the past months. But this phase of discussions cannot be drawn out interminably.
"A comprehensive deal is possible. But it can only be done on the basis of the Good Friday Agreement. The DUP must move away from the failed approaches of the past. The days of second-class citizenship, domination and humiliation are over. The British Prime Minister has a particular responsibility to impress this on the DUP leader."