The Taoiseach, Mr Ahern, has said the Provisional IRA will have to make "demonstrable commitments" to end all of its criminal activities after the PSNI blamed the paramilitary organisation for the £26.5 million Northern Bank raid.
As the prospects of early political progress dimmed, Mr Ahern said the efforts to restore power-sharing in the North had suffered a serious setback. He will discuss the situation with the British Prime Minister, Mr Tony Blair, this weekend.
The Garda Síochána confirmed last night the robbery was being investigated in the Republic. A spokesman said it was making "specific inquiries" on foot of a PSNI request. He declined to elaborate.
After the PSNI Chief Constable, Mr Hugh Orde, said yesterday that he believed the IRA was behind the raid, Mr Ahern said his greatest concern was that an operation of this magnitude was "obviously being planned at a stage when I was in negotiations with those that would know the leadership of the Provisional movement".
"The thought that when we were trying to negotiate a comprehensive deal that others, and perhaps others who were closely associated, were getting ready to have one of the biggest Christmas robberies that ever took place does nothing to help anybody's confidence," Mr Ahern said.
"This makes it difficult because it damages the levels of trust and confidence that we are trying to develop."
Mr Orde's disclosure has intensified pressure on Sinn Féin, with the Government's attention now focused on whether the party figures who took part in the talks in early December knew the raid was being planned. If they did not know, their credibility as figures who can negotiate with the IRA's authority would be questioned.
In Brussels, the Minister for Foreign Affairs, Mr Dermot Ahern, said although the robbery represented a setback to the peace process, "there have been much worse times than this, with people being bombed and murdered. We have to keep at it. We have a duty to keep at it, to copper-fasten the relative peace we have in the island," he said.
Sinn Féin, citing the word of the IRA, has continued to insist that the IRA did not carry out the robbery and complained of an attempt by so-called securocrats to "demonise and marginalise" republicans.
Most political representatives in Britain and Ireland, including the two governments, either simply rejected the republican denials or treated them with disdain.
There was general acceptance last night that the fallout from the robbery has put beyond possibility the chance of a political deal before the autumn, or probably before next year.
The PSNI and the Northern Bank have increased the estimate of the amount stolen from £22 million to £26.5 million.
The scale of the robbery has prompted the bank to withdraw most of its notes so the gang that stole them cannot use them.
However, about £4.5 million in untraceable sterling notes, other than Northern Bank notes, and about £5 million in used Northern Bank notes whose serial numbers are not known, could still be used by the robbers.
Mr Orde, after meeting the Policing Board yesterday, said he was confident the IRA was behind the robbery.
"On the basis of the investigating work we have done to date - the evidence we have collected, the information we have collected, the exhibits we have collected - and putting that all together and working through it, in my opinion the Provisional IRA were responsible for this crime, and all main lines of inquiry currently undertaken are in that direction," said Mr Orde.
