Taoiseach Bertie Ahern has said that the scourge of sectarianism, symbolised by peace walls, remains in Northern Ireland and must be tackled.
He was speaking at UCD on the legacy of the Good Friday Agreement.
Mr Ahern was welcomed to the Institute of British-Irish Studies by UCD President Hugh Brady, who paid tribute to his record as Taoiseach, particularly in the peace process.
The Taoiseach warned against complacency on the peace process.
He highlighted the failure of loyalist paramilitary groups to decommission, and he said some people remain wedded to criminality.
Mr Ahern added that there are also small unrepresentative groups on the other side who would propel Ireland back to violence.
Good Friday Agreement 'momentous'
The Taoiseach also stressed the importance of the devolution of policing and justice powers to the Northern Assembly.
To applause from the audience, the Taoiseach said that none of the violence of the Troubles had been justified, and that we should honour the dead by ensuring that violence is never again used to achieve political ends.
Speaking in advance of the conference, the Taoiseach said the Good Friday Agreement was a momentous milestone in the history of Ireland.
He said the 10th Anniversary of the signing of the agreement provides a valuable opportunity to reflect on the enormous progress made since 1998 and the future of relations on these islands.
The conference is titled From Conflict to Consensus - The Legacy of the Good Friday Agreement.
British Northern Secretary Shaun Woodward and other leading commentators on the recent history of Northern Ireland and British-Irish relations will also address the conference.
Mr Ahern is due to have a brief meeting with Northern Secretary Shaun Woodward after his address to the conference.
