The Mayor of New York, Michael Bloomberg, has unveiled a monument in Ballymote in Co Sligo dedicated to the US Army's Fighting 69th Irish regiment.
Mr Bloomberg was welcomed by members of the local community and reviewed an army guard of honour.
The monument also honours Brigadier General Michael Corcoran, a local man who commanded the regiment during the US Civil War.
A small group of anti-war campaigners staged a demonstration in the town during the ceremony.
The monument incorporates steel beams taken from the debris of New York's Twin Towers.
Ahead of today's event, the chairman of the committee which erected the monument, Fine Gael TD John Perry, said the town was honoured that Mr Bloomberg had accepted the invitation.
He said Mr Bloomberg was an extraordinary friend to New York's Irish community and it was entirely appropriate that he should unveil the monument.
However, the Sligo Anti-War Group said it was opposed to the visit because of Mr Bloomberg's endorsement of Israel's aggression in Lebanon and because of his failure to offer his sympathy to the Lebanese people.
Spokesman Tim Mulcahy said a prominent Irish-American politician of the stature of Ted Kennedy should have been invited to perform the ceremony.