The Sinn Féin president, Mr Gerry Adams, has signalled a strategy of attack being the best method of defence for his meeting with the Taoiseach, Mr Ahern, in Government Buildings, Dublin, today.
Mr Adams was insistent yesterday that the onus is on Mr Ahern to justify his claim that the Sinn Féin leadership knew in advance of the £26.5 million Northern Bank raid - rather than for the Sinn Féin president to convince the Taoiseach the IRA was not involved.
What is expected to be a difficult encounter between Mr Adams, Mr Martin McGuinness and Mr Ahern at lunchtime today marks the first of a series of meetings involving the British and Irish leaders and the Northern parties over the coming 10 days.
Moreover, on Monday the Independent Monitoring Commission will meet Mr Ahern in Dublin, with Mr Adams predicting that the governments will use the IMC - the governments' "tame donkey", he said - to penalise Sinn Féin over the Northern Bank robbery.
"Sanctions against our party won't stop our party. Sanctions against our party won't assist the peace process. All it will do is eat up more time," added Mr Adams.
After these meetings, the Taoiseach and British prime minister Mr Tony Blair, who meet next Tuesday, will assess whether in the short- to medium-term there is any way of lifting politics out of its current stalemate.
Government ministers in recent weeks have made it clear that the only possible means out of the deadlock is by the IRA demonstrably ending paramilitarism and criminality.
Mr Blair's chief spokesman last night made the same point about the meeting between Mr Adams and the prime minister at Chequers, outside London, on Thursday.
"In terms of moving forward, there can be no deal with republicans until there is an end to paramilitary activity and criminality. That is the message he gave over two years ago. He meant it then, he still means it," he said.
Chequers rather than Downing Street was chosen for the meeting to prevent republican "grandstanding" before and after the meeting, said a London source. Mr Blair is also due to meet the SDLP leader, Mr Mark Durkan, in Downing Street on Thursday.
Despite the barrage of criticism against republicans, Mr Adams was in assertive mood yesterday. He said there were just two issues that would dominate today's meeting.
"Our very reasonable request that the Taoiseach should give an explanation for his remarks. And secondly, how we continue to build this peace process. The Taoiseach does have to give an explanation. I am sorry and I am disappointed that I have to say that, but when you are in public life and you make allegations or accusations you have to stand them up, and we are looking for the Taoiseach to stand them up."
He did not want to make any further comment about the robbery. "I am beyond talking about the Northern Bank robbery. Whoever did it? That will come out in due course. The focus has to be on the consequences of this."
When asked would he have anything to say to Mr Ahern to persuade him the IRA did not carry out the bank raid, Mr Adams replied: "The convincing will be for the Taoiseach to do, and the Taoiseach has to give us an explanation as to why he said what he said. There is a debate going on about criminality and so on. What the Taoiseach has done is to have accused Martin McGuinness and I of being involved in criminality, and we want an explanation for why he made those remarks."
Mr Ahern today will also separately meet SDLP and Ulster Unionist delegations, respectively led by Mr Durkan and Mr David Trimble. On Tuesday next, Mr Ahern and Mr Blair will meet in London to take stock of the situation. On Thursday week, Mr Blair will meet Mr Trimble.
Subsequently the two leaders will assess whether there are any options for moving forward.
Meanwhile, the Northern Bank said it is carrying out a review of security procedures to try to prevent any future robberies.