A HARD border would "resurrect the memories" of militarisation during the Troubles, an influential group of Irish-Americans has claimed.
In a letter to Taoiseach Leo Varadkar and British Prime Minister Theresa May, the US Ad Hoc Committee to Protect the Good Friday Agreement warns that Brexit puts the 1998 accord in jeopardy.
The letter's signatories, who include former US Senator Gary Hart and Nancy Soderberg, a one-time adviser to President Bill Clinton, say peace in the north is "not inevitable" and that the progress in recent decades is "largely the result of the framework" established by the agreement.
"While the United States must await the outcome of the current Brexit negotiations we believe it should and must make every effort to secure and maintain the GFA which it did so much to bring about," the letter says.
"We wish to acknowledge that the EU has been and remains a steadfast supporter of the peace process and has made significant contributions to it through the well-established programs including PEACE and INTERREG."
The committee wish the taoiseach and prime minister success but say they will "remain vigilant" as the Brexit process progresses.