Talks in Belfast are concluding without securing an agreement to clear the way for the restoration of the power-sharing Executive.
Elections to the Northern Ireland Assembly may now be delayed beyond May 1st after the failure by the pro-agreement parties to secure a deal at Hillsborough Castle. The Executive has been suspended since a suspected IRA spy ring was uncovered last October.
It has just emerged that Ulster Unionist Party leader Mr David Trimble has dramatically left the talks, citing obligations in the House of Commons in London.
However, the Taoiseach, Mr Ahern, and British Prime Minister Mr Tony Blair continued to chair round table talks this evening after reporting progress at nine hours of discussions yesterday. However, a spokesman for Mr Blair said no breakthrough was likely "this side of Saint Patrick's Day".
Most of the outstanding issues, which include scaling down the huge military presence on the streets, changes to policing and the criminal justice system, have been addressed.
But demands for the IRA to empty all their secret arms dumps and republican resistance to sanctions for any future security breaches are still deadlocked.
Sinn Féin chairman Mr Mitchel McLoughlin confirmed this evening the negotiations had hit a potential stumbling block. "There was progress but there are still substantive issues that need to be resolved," he said.
Senior Ulster Unionist negotiator Mr Michael McGimpsey warned that it could be weeks before a deal was closed. He insisted that with trust in republicans running low, a mechanism had to be in place if the IRA continues its military campaign.
"The point of the exercise is to try and repair damage that has been done as a result of republican misdemeanours and we have some work still to do.
"There's work in progress but I don't expect a deal today in fact we don't expect a deal for some days or possibly weeks ahead."
Earlier, Mr Trimble said a deal may not be completed for weeks. He said he believed the talks would "peter out" without a breakthrough.
Mr Trimble said any deal would not be put to Ulster Unionists until the IRA had taken action on decommissioning and declaring that the "war is over".
"The logic of the republican position points towards them doing something. The question is: Will it be enough?," Mr Trimble asked.
"There is no question of us being able to go to the Ulster Unionist Council to look at the question of restoring institutions unless we have the clear statement from the IRA about their structure, their future, that their war is over and they have gone away," he added.
The parties have been studying a 28-page blueprint tabled by the British and Irish governments including proposals on demilitarisation, policing, criminal justice, decommissioning and IRA prisoners still at large.