Brexit should be considered an "aberration" in the bid to strengthen the peace process, US congresswoman Nancy Pelosi has said.
The US House of Representatives speaker yesterday visited the Irish border, which has become a stumbling block in the UK's withdrawal from the EU.
She was greeted by anti-Brexit campaigners during her short stop at the frontier.
The senior Democrat from California said the US had a vested interest in protecting the peace that was sealed by the Good Friday Agreement.
"We have said that we are guarantors for the agreement because we believe it is fair to both sides - that is why they agreed to it," she added.
"We believe that Brexit should be just an aberration in this discussion as we continue to build and strengthen the peace that was generated by the Good Friday accord."
Ms Pelosi repeated her assertion that the peace process was a "beacon to the world" and a model for reconciliation.
She said: "Far be it for any of us to want that beacon's lustre to be dimmed by anything that the Brexit conversation could bring down on the Good Friday accord."
The congresswoman walked across the Peace Bridge over the River Foyle in Londonderry.
It was built using EU funds and links primarily nationalist and primarily unionist communities on either side.
Ms Pelosi said her visit was made out of respect for the courage of those who helped strike the Good Friday Agreement and because of the US's links with Ireland and Northern Ireland.
The US Consulate General in Belfast was established in 1796 by the first American president, George Washington, and is the second oldest continuously operating US consulate in the world.
Ms Pelosi, who visited Belfast with her daughter more than two decades ago, said: "The difference between what we went through then and what we saw in terms of tanks and barbed wire... it is about peace - it is about not just what it means to Northern Ireland and Ireland. That would be reason enough for us to be guarantors."
She expressed pride in the work of Bill Clinton and George Mitchell, as well as senior congressman Richard Neal, all of whom worked to secure peace.
"What it means to the world... this example of reconciliation really ended hundreds of years of conflict," Ms Pelosi said.
She also repeatedly railed against the prospect of a hard border during her tour with colleagues.
Earlier this week the US congresswoman warned that trade talks with the UK could be endangered if the agreement was compromised.
The DUP's opposition to the backstop, which would keep Northern Ireland's regulations aligned with the EU to protect the free-flowing frontier, helped thwart Theresa May's bid to get her withdrawal deal through Parliament.
Some believe any reimposition of a hard border and checks at the frontier due to a no-deal Brexit could encourage a return to violence.
However, that claim is contested by many unionists.
The British Government has said it does not intend to install any border infrastructure.
Dermot O'Hara, a spokesman for Border Communities Against Brexit, greeted Ms Pelosi at the frontier.
He said: "She is saying to the British very clearly that they must respect the Good Friday Agreement, (which) underwrote the situation here.
"This is a British border here. We want the border to be in the Irish Sea and we appreciate the visit by the delegation and their support for the rights of the Irish people."
John Boyle, mayor of Derry City and Strabane District Council, said it was clear that Ms Pelosi was determined to protect the integrity of the Good Friday Agreement.
"They will support us in ensuring (Brexit) does not impact on that very important agreement signed in 1998," he stressed.
He also said a hard border would be difficult to deal with psychologically, adding: "Many of us going back generations remember what a hard border looked like here."