It would be an "immense tragedy" if Northern Ireland's peace process failed now, one of its architects said.
George Mitchell brokered the 1998 Good Friday Agreement which largely ended decades of violence and paved the way for devolved powersharing.
Northern Ireland has been without a Stormont government for months now but Mr Mitchell warned an audience in Belfast that despair fuelled instability and told people to realise that problems could be resolved.
"I urge the current political leaders and the governments in Ireland and the UK to summon the courage and vision that their predecessors summoned in 1998.
"It would be an immense tragedy if the process were to fail now after 20 years.
"Political leaders and the people of Northern Ireland have come too far to risk letting peace slip away."
Stormont has not sat since early last year amid a dispute between former coalition partners the Democratic Unionists and Sinn Fein over identity issues like the Irish language.
Former US senator Mr Mitchell later became ex-US president Barack Obama's special envoy to the Middle East, but said he would always feel a special bond with Northern Ireland.
He said: "There is no such thing as a conflict that cannot be ended.
"Conflicts are created and sustained by human beings and they can be ended by human beings."
He added: "No matter how hate-filled, peace can prevail.
"No matter how bleak the outlook, the search for peace must go on."
He received a standing ovation following his address at Queen's University.