Americans are remembering the victims of the 11 September attacks on New York and Washington and those who died in United Airlines flight 93 in Pennsylvania on the fourth anniversary of the attacks.
The names of the 2,749 victims of the twin towers attack were read out by their relatives.
Those attending the ceremony paused for a minute's silence marking the exact time four years ago when the first plane hit the north tower.
Here, the victims will be remembered at a ceremony outside the GPO in Dublin this evening.
This year ceremonies will also include prayers for the estimated one million left homeless and the thousands feared killed by Hurricane Katrina.
US President George W Bush has used the anniversary to call for a similar national response to the victims of Hurricane Katrina.
The American Red Cross says it needs 40,000 additional volunteers to help provide food, shelter and clothing to the victims of the hurricane on the Gulf Coast.
The emergency services in New Orleans said the flooding has subsided and should be drained from parishes within 40 days, half the original estimated time.
