The Defence Forces has confirmed the peacekeeper killed in Lebanon, was 23-year-old Seán Rooney from County Donegal.
The young soldier from Newtowncunningham was killed, when a hostile group attacked one of two armoured vehicles, travelling in a convoy to Beirut.
Another soldier who was seriously injured in the attack is being treated in hospital and has been named as 22-year-old Private Shane Kearney from Killeagh in County Cork.
The UN has launched a joint investigation with Lebanese armed forces into the attack last night.
However, UNIFIL told Reuters at the moment 'details are sparse and conflicting'.
In a statement, President Michael D Higgins said:
"As President of Ireland and Supreme Commander of the Defence Forces, it is with a heavy heart, and conscious of the great loss it will represent to them, that I offer my deepest condolences to the family, colleagues and friends of the member of the Defence Forces who has lost their life.
"A life lost serving the people of Ireland, serving the United Nations, and serving all those wishing for peace in our shared world.
"May I also wish a speedy recovery to those other members of the Defence Forces injured in the incident. Our thoughts are with them at this time.”
The United Nations Interim Force in Lebanon operates with 10,500 peacekeepers from 48 countries.
Over 30,000 Irish personnel have served in Lebanon since the establishment of UNIFL in 1978.
