Former US senator George Mitchell has urged political leaders in Ireland and Britain to recognise what is at stake for the future of Northern Ireland.
Mr Mitchell chaired the all-party peace talks that led to the signing of the Good Friday Agreement, the 20th anniversary of which will be marked on Tuesday.
In an interview with the BBC, he rejected claims by some that the Agreement was getting in the way of political progress in Northern Ireland now, where the Assembly has been suspended for the past year.
"I think those espousing that line are primarily concerned with the Brexit debate in the UK and are using the Northern Ireland issue as a part of that debate.
"I believe that the single most important result of the Good Friday Agreement has been 20 years of peace and surely no-one would disagree with that," he said.
"Thousands of people who might otherwise have been killed are still alive today as a consequence of the courage and vision of political leaders of Northern Ireland and of the UK and Ireland back in 1998 when they reached this agreement."
On the topic of Brexit, Mr Mitchell said it was clear that the UK and the European Union had reached agreement and publicly said there would not be a hard border.
"The difficulty, as always, is in doing what you've agreed to do.
"That's always harder and I think they're working on that now and I hope they will figure out a way to resolve it that maintains the border in the current status because that's been an important factor in reducing the stereotyping and the demonisation that existed between Northern Ireland and the Republic before, when people who lived just a short distance from the border never crossed it."
He added that the issues of the suspended Stormont Executive, Brexit and a hard border must be addressed and resolved.