Bill Clinton has warned Northern Ireland will get "whacked" if the United Kingdom votes to leave the European Union.
The former president was in the White House at the time the 1998 Good Friday agreement was signed and was one of its main architects.
Speaking in New York, Clinton said: "It’s Northern Ireland that will really get whacked if Britain withdrew from the European Union.
The Irish Times reports he added: "And I hope they don’t because it’s too easy to believe that the only solution to the problems in the world is to hunker down."
In April, President Obama is due to visit London and give his support to David Cameron's campaign to keep the UK inside the EU.
Boris Johnson, who is backing Brexit, has accused the president of "outrageous and exorbitant hypocrisy" for intervening in the debate.
But Downing Street has defended the right of foreign leaders to voice their opinion.
Obama’s spokesman has said the president would “continue to make clear” that the United States wanted to see the UK remain inside the EU.