The Fine Gael leader, Mr John Bruton, said the IRA, in the manner in which it published its latest statement, "set out, in a calculated way, to humiliate the Taoiseach, the elected leader of the Irish people, and that is not acceptable".
He criticised the fact that, as the Taoiseach was preparing to deliver a statement on the peace process in the Dail, Mr Ahern was "placed in a position where he was handed a note telling him that the entire basis upon which he was speaking had been taken away from him".
Mr Bruton said this was done "by a secret organisation which is accountable to nobody, elected by nobody and has no right to act on behalf of the Irish people".
He added that while nobody was "expecting everything stored by the IRA to be removed", the organisation could not even make a gesture on decommissioning.
The leader of the Labour Party, Mr Ruairi Quinn, said the IRA move was "a very serious blow to the peace process and can only raise further doubts about the intentions of the republican movement".
He described as "a gross act of betrayal" the fact that the statement was issued when everyone was working so hard to put the process back on track and on the eve of a crucial summit between the Taoiseach and the British Prime Minister.
"If we truly want to move forward nothing can be achieved by anyone withdrawing into their bunkers, political or military. The IRA has consistently complained of delay on the part of others. It was only on November 17th, 1999, that they finally agreed to appoint an interlocutor to the decommissioning body. It now appears that step was conditional on progress being achieved solely on their own terms," Mr Quinn said.