People and societies taking the "risk of forgiving" may be key to forging lasting reconciliation in Northern Ireland, the President Michael D Higgins has said.

President Higgins reflected on the challenges of forgiveness as he delivered a lecture in Belfast to mark the 20th anniversary of the Good Friday Agreement.

He also used the speech at Queen's University to stress the urgent need to move the stalled peace deal from the "hard shoulder" and intensify efforts to restore Stormont power-sharing.

Hailing the achievement of 1998, the president described the implementation of the agreement as a "work in progress".

"Indeed, as Northern Ireland continues to operate without an Executive, in some respects the Agreement is work which has been stalled," he added.

"It is therefore essential that we remind ourselves and reaffirm that the Good Friday Agreement, with all its imperfections and creativity, represents the best hope for all of our people, North and South.

"That is why it is now important and urgent to find a way, in Dublin and London, but above all here in Northern Ireland, to move away from the hard shoulder where the implementation of the Good Friday Agreement presently finds itself and to start moving together again along our shared journey, and to do so with generosity."

Noting the "terrible and heinous acts" of the Troubles, Mr Higgins said he offered his approach to forgiveness with "some trepidation".

"Forgiveness plays a central and necessary part in reconciliation," he said.

"I acknowledge that it is very easy to say that. Some are asked to pay a very high price when they are called to forgive, a great hurt that cannot be expelled from their memory, but their achievement is all the greater."

The president was delivering the sixth annual Harri Holkeri lecture - an event named in honour of the late Finnish statesman who played a role in peace process talks in Northern Ireland.

It was hosted by the university's Senator George J Mitchell Institute for Global Peace, Security and Justice.

Mr Higgins highlighted Bishop Desmond Tutu's belief that forgiveness had the potential to free an individual from the confines of past hurt.

"If this is true for the individual, then perhaps it can also be true for societies, and this of course was at the centre of Bishop Tutu's thinking in his thoughts as to how to construct a decent future for the people of South Africa following the years of brutality and atrocities," he said.

"Forgiveness cannot occur without a commitment to remember, as difficult as it may be, the actions of the past. I therefore welcome the launch earlier this month of the British Government's consultation on Addressing the Legacy of Northern Ireland's Past.

"The full implementation of the Stormont House Agreement, of which the consultation forms part, will be an important step towards on-going reconciliation in Northern Ireland," he said.