The Labour leader, Mr Ruair∅ Quinn, called for the decommissioning of IRA weapons.
He said the republican movement was at the crossroads and must decide which direction it was now going to take.
"I would urge the republican movement to cross their Rubicon, to state fully, unequivocally and unconditionally that their war is over, that they are fully wedded to the democratic system and that they will ensure the early decommissioning of their paramilitary weapons."
Urging caution in the American response to the New York atrocity, he said it was perfectly understandable that, in the US and elsewhere, there was a wish to lash out in response to terrible acts.
"Indeed, I think it would be unreasonable not to expect the US to respond to this unprecedented assault on its people. They clearly have the right and the responsibility to do all in their power to prevent similar attacks into the future.
"But I would urge very strongly whatever is done should be done in accordance with international law and on the basis of the greatest degree of international consensus." He said restraint in the face of provocation and assault was not a sign of weakness but of strength.
"I believe that the objective should be to bring to justice those responsible and to see the destruction of the organisation and apparatus used to organise and carry out these evil deeds.
"Most of all, we must try to ensure that innocent people should not be made to suffer and should not be made to die for something over which they had no influence and no control." Mr Quinn said that for the authorities in Afghanistan the handing over of Osama bin Laden should not be an issue. He should already be in the custody of the United Nations.
"And it also goes without saying that the right to self-defence is not an absolute one, and that the exercise of that right must itself be in conformity with the requirements of international law.
"There has been much talk of the vengeance and wrath of America. I do not hesitate to say that vengeance and wrath, even in response to last week's outrages, are not a basis for military action. The international community seeks peace, security and justice, not revenge." It would be a good time, said Mr Quinn, for Ireland to reassess its degree of adherence to the principles of international peaceful co-operation, if only because the commitment of the international community to them would be tested in the weeks and months ahead.
"The most glaring gap is our failure to recognise the International Court of Justice. As members of the UN we, like all other members, are parties to the Statute of the Court, but we have never made the necessary declaration recognising the court's jurisdiction.
"Our calls as a member, or as president of the Security Council, for peaceful resolution of disputes will ring a little hollow when we ourselves have failed to sign on to the principal judicial means for bringing about that peaceful resolution.
"Nor have we ratified the European convention on the peaceful resolution of disputes, even though we helped to draft it," he said.