First Minister Arlene Foster was joined by Taoiseach Enda Kenny at the annual Remembrance Service in Enniskillen.
Taoiseach Enda Kenny joined First Minister Arlene Foster for the annual wreath-laying ceremony at Enniskillen - where 29 years ago an IRA bomb killed 11 people and injured dozens of others.
A 12th victim of the outrage died 13 years later having never woken from a coma.
Mr Kenny has taken part in the ceremony every year since 2012 and laid a wreath of green laurels alongside the many red poppies at the Co Fermanagh town's war memorial.
His annual presence is symbolic of the greater recognition now afforded in the Republic of Ireland to those Irishmen who fought and died serving in the British Army in the First World War.
There were no discussions between the two leaders who are expected to meet more formally this week in Dublin on Tuesday and again in Armagh, where Brexit is likely to dominate the agenda of Friday's north/south ministerial council meeting.
The biggest Remembrance Sunday event took place in Belfast, where more than 1,000 people turned out to pay their respects at the city cenotaph.
Past and present members of the armed services marched alongside members of the Royal British Legion and other military associations past rows of small wooden crosses through the Garden of Remembrance.
Some of the crosses had photographs of servicemen and women killed in more recent conflicts, including in Iraq and Afghanistan.
Senior police officers, representatives from the emergency services and the French honorary consul Regine McCullough also took part.
Irish Tanaiste Frances Fitzgerald laid a laurel wreath.
Speaking afterwards, Ms Fitzgerald, whose grandfather served as a soldier in the British Army and whose father was a colonel in the Irish Army, said it had been an important engagement.
She said: "So many people across the island lost their lives; 50,000 families affected by loss of a loved one during the First World War.
"We have had a government minister here since 2012 and I think it is really important to come together, to remember together and to look at our shared histories."
Commemorations in Belfast were led by the city's Lord Mayor Brian Kingston. On Friday about 1,000 took part in a two-minute silence at City Hall to mark Armistice Day.
Meanwhile, James Brokenshire laid a wreath as Northern Ireland Secretary for the first time.
He said: "I think it is extraordinary, that rightfully we bring together the whole community remembering those who gave their lives for us in that sense of service and sacrifice, for freedom, for liberty.
"I think that remains as relevant now as it has ever done."
Mr Brokenshire also commended the Irish Government for sending a representative.
He added: "It was very good to see Frances Fitzgerald here in Belfast.
"There is that shared history that increasingly we are able to recognise and be part of; to underline all of those who served from across the island of Ireland who served in the Great War and who lost their lives in seeking to fight for freedom and for liberty."