The events of September 11th last have "touched us all", the Taoiseach told a commemoration ceremony at the US Embassy in Dublin yesterday.
"We remember today over 3,000 people who lost their lives, the many who were injured, and their families and friends," Mr Ahern said.
"And among them we remember too, in a special way, the Irish and those of Irish descent who lost their lives on that terrible day.
"What happened on September 11 touched us all. It was deeply traumatising for the people of the United States and its repercussions have been felt throughout the entire international community".
At a ceremony in the grounds of the US Embassy in Ballsbridge members of the Dublin Fire brigade laid a wreath. A message on the US embassy website thanks the Irish people for their support over the last year.
A statement form President McAleese said the passage of time had not lessened the "enduring, shocking, images of the cruel atrocities" which were visited on the United States. Mrs McAleese was in Co Fermanagh where she observed a minute's silence at the Enniskillen Rotary Club at 1.46 p.m.
"Our American friends, among them so many members of our Irish family, were sorely tested that day," her statement said.
"Today we reflect with admiration and respect on the courage, selflessness, resilience and fortitude with which they responded to that tidal wave of agony, which broke over them but did not break them".
Earlier Mr Ahern, and members of the Government and Opposition, attended a service at the Catholic Pro-Cathedral in Dublin which began at 11 a.m.
In the North, First Minister David Trimble and Deputy First Minister Mark Durkan attended memorial services.