The President and the Taoiseach will attend a special service in Omagh on Saturday afternoon for the victims and bereaved. Mrs McAleese will attend a service the following day in St Patrick's Cathedral in Dublin at 3.15 p.m.
The Government has urged the public to participate in similar acts of prayer on Saturday and to observe a minute's silence at 3.10 p.m., the time of the explosion. In Galway on Saturday there will be an open-air ecumenical service in Eyre Square at 3 p.m. Tonight there will be a concelebrated Mass in Galway Cathedral at 8 p.m.
The Government is to fly the national flag at half-mast on all State buildings until after Saturday's service in Omagh. It has asked all organisations flying the national flag to do likewise. The Archbishop of Armagh, Dr Sean Brady, will sign the book of condolences at Armagh City and District Council offices this morning. Mrs McAleese and her family signed the book at the Mansion House in Dublin yesterday and it remains open for signing.
The GAA said the Omagh tragedy will be "acknowledged and remembered with dignity at next weekend's games".
The Workers' Party has organised a public vigil in the Peace Garden, Christchurch Place, for Saturday at 3.10 p.m.
The Irish Times opened a book of condolences on its website yesterday afternoon. Mr Conor Pope of the paper's electronic publishing division said that within minutes it had received 500 calls from around the world. By last night that had risen to 1,000.
The website will remain open until Saturday and the messages will be sent to Omagh District Council.
Ms Ann Gormley, a Dublin woman who lost a relation in the Miami Showband massacre in 1975, said her daughter had opened a site on her company's computer. By yesterday they had received messages of support from 4,000 companies around the world.
RTE also opened an on-line book of condolences. The station's Internet producer, Mr Paul Russell, said: "It occurred to me as I heard books were being opened all over the country that it might be a good idea to open an on-line book which would allow those who can't get to the signing centres or who live outside Ireland to send their messages".
Northern Ireland Global Gateway has also opened a book of condolences on the Internet and has undertaken to send all messages received to the people of Omagh through their local authority as well as to the British and Irish governments and all members of the Northern Ireland Assembly.