Northern Ireland and the Republic must co-operate economically to face global challenges, the Taoiseach has said.
"This is not a political statement. This is common sense," Mr Ahern told a conference on North-South bodies organised by the Institute for British-Irish Studies.
"Europe, and Ireland within Europe, must work even more closely together if we are to keep our peoples at work and our economies thriving.
"The greatest competition that we face comes not from within the borders of the EU, or this island. It comes from further afield - from China, from India and Asia generally," he said.
It was "hugely regrettable" that North-South bodies set up under the Good Friday agreement had not been able to operate fully because of the suspension of the NI Assembly and Executive, Mr Ahern said.
"I look forward to the day when representatives of the NI parties are back again around the North-South Ministerial Council table with us," he said.
The Government's support for the Belfast Agreement was "rock solid", he went on.
"We will work in every way that we can to ensure its full implementation and restore all of its institutions to operating capacity. This is not just political mantra.
"I am saying it because I am entirely convinced of the inescapable logic of the agreement," the Taoiseach told the conference at University College Dublin.
However, he said he would not be able to go back to encourage the DUP to re-engage unless the IRA ended all activity and decommissioned. "I will not be going back to Ian Paisley to ask him to become involved if I cannot answer the questions about decommissioning, about criminality," he said.
Questioned about the timing of the IRA's response to the call on it made by the Sinn Féin leader, Gerry Adams, to follow a political path, Mr Ahern said: "I can't put a timescale on 'soon', but, yes, I do think we will get that answer over the summer.
"I have no idea what that answer will be, but I am certain that the internal debate on an all-Ireland basis is comprehensively under way, and that is a good thing.
"That engagement, involving all of the members of the republican movement, the activists of the republican movement, is what can at least help us to come to finality if the answer is positive.
"If it is negative we have a different issue to deal with. But I am an optimist on these matters. I hope that it is positive, I hope that it is conclusive.
"I hope that there is no ambiguity about it, that there are no fudges in it.
"If that is the case then I believe we deserve a response from unionism to move back within the framework of the agreement.
"I think it is helpful if we get it this summer. If it feeds into the marching season in a positive way that is even better."
