Northern Ireland's political leaders know the "right thing to do" and should "get on and do it", former Prime Minister Sir Tony Blair has said.
He was appearing alongside former US president Bill Clinton and ex-Taoiseach Bertie Ahern at a major conference in Belfast marking the 25th anniversary of the Good Friday Agreement.
Mr Clinton told how politicians "winged it" to help secure the historic peace deal in 1998, while Mr Ahern said he hoped the DUP would allow Stormont's power-sharing institutions to be restored.
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Former US secretary of state Hillary Clinton, who is hosting the conference at Queen’s University in her role as chancellor, chaired the panel discussion between the three former leaders.
Prime Minister Rishi Sunak and Taoiseach Leo Varadkar are due to attend the conference later in the week.
Earlier George Mitchell, who chaired the talks which led to the 1998 agreement, urged Stormont leaders to act with the same "courage and wisdom" as their predecessors.
A bust of the former US senator was unveiled in the grounds of the university as part of the Agreement 25 conference.
Sir Tony said the peace that resulted from the agreement "isn't perfect" but Northern Ireland is a "much better place than it was before".
He added: "And the only thing I would say to today’s leaders is I think when you stand back and you reflect, you know in your heart of hearts, what the right thing to do is, and you should just get on and do it."
Mr Ahern said the alternatives to the agreement are "not good", adding: "Let’s hope they (the DUP) listen to what George Mitchell said today, and listen to what we’re saying, that we all just get back on the track.
"There’s too many big things to be dealing with than to be arguing about some detail that was caused over something or another, which I’m not sure what it is even."
He added: "So just let’s move forward and try and make this work."
Mr Clinton told the conference the Good Friday Agreement came about because political leaders decided the "time was right to do the right thing".
He said: "There were days I felt like I was taking Seamus Heaney’s advice to take a flying leap and walk on air against your better judgment.
"That’s how it started. We all just decided that the time was right to do the right thing."
The former US president said people thought they were crazy to believe they could get paramilitaries to decommission their arms.
"We'd like to tell you that we had it all thought through but the truth is we made up a lot of it as we went along, we had to wing it," he said.
The Good Friday Agreement largely ended Northern Ireland's 30-year sectarian conflict known as the Troubles.
Its anniversary comes at a time when Stormont's power-sharing institutions established from the agreement have collapsed, as the DUP is blocking them in protest against Brexit's Northern Ireland Protocol.
The UK and European recently agreed the Windsor Framework in a bid to reduce barriers to trade between Great Britain and Northern Ireland created under the protocol.
While the DUP says the framework has gone some way to address its concerns about the protocol, it says significant issues remain.
In a keynote address at the conference, former US senator Mr Mitchell said the people of Northern Ireland and their political leaders "changed history" 25 years ago.
He said: “When you approved the agreement you were also talking to Israelis and Palestinians, to Colombians, to Africans, Asians, to Americans – in fact you were talking to the world.
"This is an agreement for peace and for the future, not just here, but everywhere."
Mr Mitchell acknowledged that people in Northern Ireland continue to "wrestle with their doubts, their differences, their disagreements".
But he added: "The answer is not perfection or permanence, it is now, as it was then, for the current and future leaders of Northern Ireland to act with courage and vision as their predecessors did 25 years ago.
"To find workable answers to the daily problems of the present, to preserve peace.
"To leave to the next generation peace, freedom, opportunity and the hope of a better future for their children."
Mrs Clinton said the Windsor Framework provided Northern Ireland with an opportunity to become an economic hub for global trade and investment.
She said: "You know, we are at a standstill with the Northern Ireland Assembly no longer functioning. But the Windsor agreement provides a path forward not just for convening but for positioning Northern Ireland as an economic hub for global trade and investment through privileged access to the UK and all of its trading partners, as well as the EU."
She added: “There have been many moments in Northern Ireland’s peace journey where progress seemed difficult, when every route forward looked blocked, there seemed nowhere to go.
“But you have always found a way through and I believe you will again, because the stakes for the people of Northern Ireland are so high.
"You stand as an example to the world of how even the staunchest adversaries can overcome differences to work together for the common and greater good.
"So, I encourage everyone now to move forward with the same spirit of unstoppable grit and resolve that brought the peace 25 years ago. Your friends in the United States will be behind you all the way as you work toward peace, prosperity and stability that lasts."
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