The "political and diplomatic fall-out" from the invasion of Iraq will be "immense", the Minister for Foreign Affairs, Mr Cowen, has told the British/Irish Inter-Parliamentary Body (BIIPB).
"Only one thing is certain - there will be far-reaching change, both in Iraq and the surrounding region and in the wider international order," he said, acknowledging that the war has caused "sincere differences" of opinion.
Hoping that casualties and destruction could be "minimised and contained", he said there would inevitably be losses and tragedies, both for Iraqis and coalition troops.
A small group chanting anti-war slogans demonstrated outside the Ormonde Hotel in Kilkenny, which is hosting the six-monthly plenary meeting of the BIIPB.
Questioned about civilian casualties, Mr Cowen said the decision to let the US use Shannon Airport and Irish airspace did not compromise Irish neutrality.
During a debate on Northern Ireland, every TD and senator who spoke bar Sinn Féin Louth TD Mr Arthur Morgan expressed sympathy with the families of British soldiers killed in the war.
Fine Gael Cavan Monaghan TD Mr Seymour Crawford said thousands of Irishmen have "laid down their lives with the British armed forces in different conflicts" over the years.
Expressing sympathies for the British losses, Fianna Fáil Clare TD Mr Tony Killeen said "the truly distressing images" in Iraq were not long ago emerging from Northern Ireland.
British Labour MP Mr Harry Barnes said while he disagreed with Mr Blair on Iraq, Mr Blair's approach on the North has worked "fantastically well".