Sinn Féin President Mr Gerry Adams has told the party's ard feis that terrorism is "ethically indefensible".
The party's president said the terror attacks on the US have set back the cause of other struggles around the world.
He told the Dublin conference the attacks were inexcusable and called on those behind them to be brought to justice.
Mr Adams said: "Terrorism is ethically indefensible. Those responsible for the atrocities in the United States must be brought to justice.
"What happened in New York and Washington and Pennsylvania was, as the UN Human Rights Commissioner and former Irish President Mrs Mary Robinson said a crime against humanity. Progressive struggles throughout the world have been set back by the attacks in the USA.
"There is no excuse, no justification for those type of actions but neither should anyone who is truly concerned with world peace be deflected from the task or be carried away by the notion of a clash between civilisations.
"The real challenges is for dialogue, not retribution. That is the lesson of the peace process on this island."
The West Belfast MP acknowledged the peace process was in a "mess".
With unionists planning an exclusion motion in the Stormont Assembly against Sinn Féin ministers in the power-sharing government, he insisted his party would not give up on the Northern Ireland peace process.
Mr Adams also said the weapons issue could be solved.
PA