US President Barack Obama cannot cross the border into Northern Ireland during his Irish trip unless he first travels to London, Taoiseach Enda Kenny has said.
The Government is gearing up for the historic May visit after President Obama announced on St Patrick's Day that he wanted to return to his roots in Moneygall, Co Offaly.
But the Taoiseach said that under diplomatic rules the president cannot cross the border without first setting foot in Britain.
"The problem actually is that the president, under existing protocol, he's not allowed to go to Northern Ireland without first having to go to Britain," Mr Kenny said.
"So if President Obama were to decide to go close to the border, actually from a protocol perspective he's expected to go to London before he would go to Northern Ireland."
Although no date has been confirmed for the trip, it has been speculated the president wants to arrive before a planned state visit to Britain on May 24.
Northern Ireland First Minister Peter Robinson and Deputy First Minister Martin McGuinness have raised the possibility of a visit to Northern Ireland with Mr Kenny.
Civil rights campaigner Jesse Jackson has also advised President Obama to go north, claiming the soul of the island was in Belfast and Derry.
In the Dail Sinn Fein President Gerry Adams, who topped the poll in Co Louth, asked if the world's most powerful political leader could stop off in his border constituency, while travelling to his native west Belfast.
Mr Kenny said the issue was out of his hands, continuing: "But I'm very glad he's coming here and I hope that the people of Ireland will give him a brilliant and wonderful welcome as he comes to associate himself with part of his ancestry."