Sinn Féin president Gerry Adams has protested to the US administration about airport security procedures which caused him to miss an event on his St Patrick's week itinerary.
Mr Adams, accompanied by Richard McAuley and Rita O'Hare, was delayed by screening procedures at Dulles airport, Washington DC when they arrived for a flight to Buffalo, New York on Friday.
They had been invited to Buffalo's Irish Centre by Congressman Brian Higgins. On hearing of Mr Adams's delay, the Democrat congressman told the audience Mr Adams was absent because his name was on a "terror watch list" and should not have been.
However, Homeland Security officials would not comment on this. It is understood this is the first time Mr Adams has been detained while in the US since he started receiving visa waivers in 1994.
Mr Higgins visited Ireland in January as part of a Friends of Ireland delegation for talks in Belfast and Dublin.
Speaking from the US, Mr Adams said: "I am deeply disappointed that I could not attend the events in Buffalo - 700 people turned up to be briefed on the peace process.
"I have consistently raised with the administration the problem of additional security screening. While I understand the need for vigilance, Sinn Féin members are the victims of an unacceptable and unfair administrative practice. We have protested again to the administration."
However, United Airlines said there were two factors behind the incident - namely the extra security and the time that the Sinn Féin members arrived to check in. The airline claimed that Mr Adams and his party arrived at the ticket desk at 4.29pm for a flight scheduled to take off at 5.10pm.
Spokesman Robin Urbanski claimed that the three Sinn Féin members had left "a very, very, very short time to go from point A to point B".
He added that this was especially true given the usual Friday evening rush. Mr Adams and his colleagues were cleared for check-in, he said, but by this time the flight was departing.
A Sinn Féin spokesman in Belfast told The Irish Times last night that no party member should be on any additional security list in the US.
The Government declined to comment on the incident. A spokeswoman said the issue was "a matter for the US authorities".