The Taoiseach Mr Ahern tonight renewed the Government's commitment to "full engagement" in the European Union at a function in honour of visiting Commission President Romano Prodi.
But in issuing the pledge he also highlighted the importance of the "nation state" within the community.
Mr Ahern declared: "Support for the EU and Ireland's full engagement in it is a fundamental cornerstone of government policy.
"Ireland's present and future success is indissolubly bound up with the European Union.
"The challenge for both the Union and for Ireland - and, indeed, every other member state - is to ensure that the interests of the people and the interests of the Union as a whole stay aligned, and do not begin to diverge.
Mr Ahern added the warning, however: "While there is a growing sense of a shared European identity, the basic building block of Europe - the core political reality - is the nation state.
"It is with their own country and their own national institutions that people across Europe, including in Ireland, most directly and most powerfully identify.
"The evolution of the Union must be consistent with that reality."
Earlier Mr Prodi said the Nice Treaty must be ratified in order to make an enlarged Europe work. Speaking outside Government Buildings after a meeting with the Taoiseach, Mr Prodi said the Treaty needs to be ratified by all 15 members.
He said he was not surprised that some people had reservations about the Treaty. He said Ireland had "nothing to lose" by entering an enlarged Europe with its identity intact.
Significantly he warned Treaty of Nice will not be renegotiated.He said: "The Nice Treaty is the Nice Treaty.
"You can't change a treaty that has been decided by all the countries."
Mr Prodi sparked confusion earlier in the day by suggesting EU enlargement could go ahead without the Nice Treaty, only to say later this was not possible.
In an interview in today's Irish Times, Mr Prodi said the issues of enlargement and the ratification of the Nice Treaty should be treated separately.
However in the Dail today the Taoiseach clarified Mr Prodi’s remarks saying while the Nice Treaty is necessary politically for EU enlargement it is not a legal prerequisite.
Tomorrow Mr Prodi is due to meet representatives of groups opposed to the Nice treaty.
Additional reporting by Reuters/PA