The border arrangement with Northern Ireland could be destroyed by Brexit, according to Luxembourg's Foreign Minister Jean Asselborn.
Mr Asselborn met with Minister Charlie Flanagan earlier and is being brought to see the border this afternoon.
He said the border issue for Ireland will be a key one during the Brexit negotiations.
Mr Asselborn said the UK's decision to leave the European Union poses a threat.
"If a country leaves the European Union this cannot mean that peace in Europe is no more protected.
"If a country leaves the European Union this cannot mean that peace in Europe is no longer protected.
"I am aware that we need a lot of sensitivity."