DUP leader Arlene Foster and Irish Government minister Heather Humphreys have both laid wreaths at the cenotaph in Enniskillen.
Hundreds gathered in the narrow streets to watch a musical procession including a brass band and bagpipes before representatives of the four main churches in the town led a service.
Remembrance Sunday in the Co Fermanagh town has an added poignancy after a Provisional IRA bomb devastated the event in 1987.
Eleven people were killed in the blast. A 12th victim, Ronnie Hill, slipped into a coma two days afterwards and died 13 years later.
A number of families of the bomb victims were present in Enniskillen for the ceremony.
Armistice commemorations started before dawn in the town - which is among the most westerly in the United Kingdom - with a lone piper playing at an event at Enniskillen Castle ay 6am.
The Last Post was played on the bugle that sounded the charge of the 36th Ulster Division at the Battle of the Somme in 1916, before a two-minute silence was observed.
One of the biggest events in the region on Sunday took place at the cenotaph at Belfast City Hall.
It was attended by Northern Ireland Secretary Karen Bradley and Ireland’s deputy premier Simon Coveney.
Representatives of all the main churches were present as well as the armed forces and Police Service of Northern Ireland Deputy Chief Constable Stephen Martin.
Sinn Fein’s Belfast Lord Mayor Deirdre Hargey was not in attendence.
A party spokesman said that its representatives will not take part in events which “celebrate or attempt to legitimise British imperialism”.
Deputy Lord Mayor Emmet McDonough-Brown instead represented the city.
Sinn Fein vice president Michelle O’Neill will attend an Armistice service at St Patrick’s Cathedral in Dublin.
A special service to mark the centenary of Armistice Day will be held at St Anne’s cathedral on Sunday afternoon.
Mrs Bradley and Democratic Unionist MP Jeffrey Donaldson are set to be among guests at the service during which poet Michael Longley is set to read his work Ceasefire.
Mr Coveney was not present at the service due to the inauguration of Michael D Higgins for his second term as Irish president in Dublin.
In a letter published in the order of service, Mr Coveney said: “For far too long remembrance of the war on the island was a source of division. There was a sense that commemoration of the young Irishmen who died in the Somme or Gallipoli was a political declaration, or a marker of community identity.”
“In recent times, and as we have marked the centenaries of the events of that decade, we have seen something very different. We have seen leadership and scholarship and sensitivity and generosity.”