Memorial services will take place on Saturday and Sunday in Omagh to mark the first anniversary of the bomb attack by dissident republicans in the Co Tyrone town.
A spokeswoman for the organising committee in Omagh said the main service on Sunday afternoon would "include a minute's silence at 3.10 p.m. to coincide with the year to the day of the bomb attack". The service would be "an open ceremony so anyone who wishes to attend can come along to pay their respects", she said. The bomb killed 29 people and left some 300 injured.
Several politicians including the Northern Ireland Secretary, Dr Mo Mowlam, will be in Omagh on Sunday. The Government is expected to be represented by the Minister for State for Foreign Affairs, Ms Liz O'Donnell.
It is understood that the service on Sunday will be a "low-key affair" out of respect for the wishes of the relatives of those who died.
The President, Mrs McAleese, will be represented at a service on Sunday in Dublin's Pro-Cathedral by her aide-de-camp. Mrs McAleese is on holidays in Ireland and will not be attending any of the weekend services.
A Government spokesman said the Taoiseach, Mr Ahern, would attend the Pro-Cathedral service. The Government Chief Whip, Mr Seamus Brennan, is also expected to attend.
A spokesman for the British royal family said "no details were available, as of yet, as to whether a member of the royal family would be travelling to Omagh".