A number of services have been arranged in Dublin to allow people to pray for those killed, injured and bereaved by the terrorist attacks in the US.
A Vigil of Prayer for Remembrance and Reconciliation will take place in the Pro-Cathedral today at 8 p.m.
The President, Mrs McAleese, and the Taoiseach, Mr Ahern, will both attend an Ecumenical Service of Remembrance at the Pro-Cathedral tomorrow at 10.45 a.m.
Three minutes' silence will be observed throughout the State at 11 a.m.
In response to the Government's declaration of a National Day of Mourning, the Archbishop of Dublin, Cardinal Desmond Connell, is requesting that Masses or prayer services be organised in each of the 200 parishes of the Dublin diocese tomorrow to coincide with the Ecumenical Service.
Cardinal Connell will celebrate Mass in the Pro-Cathedral on Sunday, September 16th, at 12.30 p.m. to remember the victims of the terrorist attacks.
The President, Mrs McAleese, and the Taoiseach, Mr Ahern, will be in attendance.
Meanwhile, the Islamic Foundation of Ireland has appealed to people not to "rush to judgement" in the aftermath of the attacks.
"Let the response be mature and thoughtful.
It is important people know that Islam means peace and that as Muslims we condemn this terrorist action."
The statement from the Islamic Foundation of Ireland continued: "...We extend our most heartfelt condolences to the victims of the nightmarish terror ... and to their families".