The Taoiseach and the British Prime Minister will take personal charge of talks in Belfast after Mr David Trimble's expected resignation as the North's First Minister on Sunday.
Mr Ahern and Mr Blair will travel to Northern Ireland, probably in about 10 days, to steer a final push to avert the collapse of the political institutions. They may head up the talks for several days.
After all parties agreed to join the new talks yesterday, Mr Blair said these would be "intense negotiations". Both governments are determined to bring the issue to a head by mid-July, and see the six-week breathing space available after Mr Trimble's expected resignation on Sunday as too long.
"We can't go on endlessly," the Taoiseach remarked at a press conference last night. "It was quite clear today that there were no new arguments. . .now we really have to try to see if we can reach a conclusion."
Mr Trimble confirmed yesterday that he fully expects to have to carry out his threat to resign on Sunday over the IRA's failure to move on the arms issue.
He is likely to nominate UUP Minister Sir Reg Empey to carry out his functions which, under legislation, would allow six weeks before the political institutions collapse.
However, the climax of the North's marching season on July 12th, coupled with the Taoiseach's departure for a 10day official visit to South America on July 16th, add to the urgency.
Hopes for a breakthrough last night centred on speculation that once Mr Trimble has carried out his threat, the IRA may be willing to show some flexibility.
All participants in yesterday's talks at Hillsborough Castle now accept that the IRA will live up to its pledge not to respond to deadlines set by Mr Trimble.
The two governments, the SDLP and the UUP all maintain that an IRA move on decommissioning is the key to progress on the other outstanding issues: demilitarisation, police reform and the stability of the political institutions.
The post-resignation talks will begin next week in Belfast, co-chaired by Minister for Foreign Affairs, Mr Cowen and Northern Secretary, Dr John Reid. Unless they determine that there is no prospect of agreement, Mr Ahern and Mr Blair may devote several days - probably the following week in the run-up to July 12th - to trying to hammer out a deal.
Sinn Fein leaders told the two governments yesterday there was no prospect of any move on decommissioning before Sunday.
The chairman of the International Decommissioning Body, General John De Chastelain, is expected to confirm in the next few days that no IRA arms decommissioning has taken place. Mr Trimble warned last night that the absence of progress in the next six weeks would inevitably lead to "collapse" of the institutions.
However, the executive will continue to operate - possibly for a further six weeks - after Mr Trimble's expected appointment of Sir Reg Empey to exercise the First Minister's functions after his resignation.
Under the Northern Ireland Act 1998, Sir Reg can exercise these functions up to August 12th. Deputy First Minister Mr Seamus Mallon will also continue to exercise his functions for six weeks, although ceasing to hold office.
However, the UUP was keen last night to ensure that talk of the Executive continuing to operate normally would not dilute the sense of crisis. Mr Trimble became angry when asked by reporters about the arrangements to be put in place and accused those attaching significance to them of "chasing after trivia".
The remaining UUP Ministers are expected to remain in place in the immediate aftermath of Mr Trimble's resignation.