Defence forces took part in a military parade in Dublin

In Belfast, Sinn Fein leader Gerry Adams led a parade to the republican plot in Milltown Cemetery.

There were also speeches and wreath-laying ceremonies in Armagh, Tyrone, Londonderry and Donegal.

In Dublin, tens of thousands gathered to watch a 2,500 strong military parade through the city centre.

It was the city's first Easter Rising parade for 35 years and was the largest ever ceremonial duty undertaken by the Irish army.

The parade, which began at Dublin Castle, made its way along Dame Street, College Green and Westmoreland Street before crossing the River Liffey on to O'Connell Street.

Irish President Mary McAleese joined Taoiseach Bertie Ahern at the front of the General Post Office on O'Connell Street, the spot where the rebellion began.

Commemoration

The Irish flag above the building was lowered to half mast and Captain Tom Ryan, of the sixth Infantry Battalion, re-enacted the reading of the Proclamation of the Republic.

President McAleese inspected a guard of honour before laying a wreath in commemoration of all civilian and military personnel, including the British, killed in 1916.

Ceremonies to mark the rising began earlier on Sunday when Mr Ahern laid a wreath in Kilmainham Jail as a mark of respect to the men executed after the revolt.

In a speech, Mr Ahern called for reconciliation amongst the people on the island of Ireland.

"Today is a day of remembrance, reconciliation and renewal," Mr Ahern said.

Heavy fighting took place in central Dublin in 1916

"As we look to the future, we must be generous and inclusive so that all of the people of Ireland can live together with each other and with our neighbours in Great Britain on a basis of friendship, respect, equality and partnership.

"And every day, in every place, we will continue to work for peace, for justice, for prosperity and for reconciliation between all who share and who love this special island."

In the early 1970s, during the Troubles in Northern Ireland, the military parades were stopped and official commemorations became more low key.

BBC Dublin correspondent James Helm said Sunday's parade had stirred up debate about the revolt and how Dublin should mark its anniversary.

Mr Ahern made the decision to hold the parade in the autumn, and the decision drew some criticism.

"Some question the military involvement in the parades, while others have accused him of trying to make gains from his political opponents - Sinn Fein - who've long seen themselves as 'heirs' to the memory of 1916," he said.

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The 1916 Easter Rising saw Irish rebels attempt to seize the capital from British imperial forces.

British troops put down the rebellion and many of its ringleaders were captured and executed.