The President of the European Parliament, Mr Pat Cox, said he was "sickened" at the "reductionism" of a wonderful moment in history - the EU enlargement - through tabloid stories about "floods of migrants".
Mr Cox was speaking in Dublin Castle at a joint press conference held by the presidents of the EU Commission, the European Parliament and the European Council.
He was asked by a journalist about fears being expressed in some EU states about the effects of the enlargement.
Pat Cox speaking at Dublin Castle this morning
Mr Cox said we must be "evidence-led and not prejudice-led" in assessing the issues involved and that where there was prejudice it must be confronted.
Mr Cox also warned against rushing into a new referendum in Cyprus following last week's rejection by the Greek Cypriot community of a referendum on unification of the divided island.
He said the EUR259 million earmarked by the European Union for Cyprus would go to the northern part of the Island in the event of a settlement and would be used to promote economic development.
Mr Cox, along with the Taoiseach and the President of the European Commission Mr Romano Prodi spoke of the challenges facing the enlarged EU, in particular the challenge posed by the new EU constitution.
Mr Ahern said it was always going to be challenging to explain and win support for the constitution, but that the three presidents and the Irish presidency would play their part in that.
In his address, Mr Prodi said enlargement of the EU was a "win-win" exercise for all peoples of the continent. However, there was "much unfinished business" to attend to. He said the "disappointing" referendum result in Cyprus demonstrated that the achievement of the grand goal of a broad-based European unification could still be undermined by unresolved regional concerns.
In addition, he said that despite its growth by one fifth geographically and in population virtually overnight, the Union "neither should, nor can withdraw into smug satisfaction at its achievement". There were other candidates for EU membership whose aspirations must be given due consideration.
The Commission has recommended opening negotiations with Croatia and negotiations are already underway with Bulgaria and Romania. The three presidents indicated that a decision on opening negotiations with Turkey is due to be taken before the end of the year.