The Taoiseach's plans for Northern Ireland Assembly members to attend 1916 Easter Rising and Battle of the Somme commemorations were dealt a blow today after they were rejected by the Ulster Unionists.
Mr Ahern had invited Stormont MLAs to witness a military ceremony at the GPO in to mark the 90th anniversary of the 1916 Rising.
The MLAs were also be invited to attend a 90th anniversary ceremony in June for the thousands of soldiers killed in the First World War Battle of the Somme at the Islandbridge War Memorial.
However, after a meeting of his party's Assembly Group, Ulster Unionist parades spokesman Michael Copeland said although they welcomed the Government's plans to commemorate the Somme, they viewed the 1916 Easter Rising as an act of terrorism.
Mr Copeland said the UUP fully respected the right of people in the Republic to commemorate events in their history in whatever way they deemed appropriate.
He added: "We also recognise the very great steps being taken to honour the memory of the true heroes of 1916 (those serving in the 36th (Ulster), 16th (Irish), 10th (Irish) and other commonwealth and empire forces. We regret that on this occasion we must decline Mr Ahern's invitation.
A spokesman for the SDLP said its MLAs would be attending the commemoration.
The Government has said the main 1916 commemoration would encompass a military parade reflecting the changing role of the Irish Defence Forces and their significant representation as United Nations peacekeepers abroad. Garda involvement in UN missions would also be reflected.
Details of the Islandbridge commemoration for the Battle of the Somme have yet to be released.
Unionists have been critical of plans by Derry City Council to mark the 1916 Rising. After the council approved plans for a commemoration, DUP Assembly member Willie Hay said unionists in the city could not participate in any ceremony.
PA