Brexit: EU backs Dublin on open Northern Ireland border
The European Commission president has said he agrees with the Irish government that Brexit should not bring back a "hard" Northern Ireland border.
"We don't want to have hard borders between Northern Ireland and the Republic," said Jean-Claude Juncker.
He was speaking after talks in Brussels with Irish Prime Minister (Taoiseach) Enda Kenny. The UK is expected to trigger the Brexit process next month.
Border controls were removed under the 1998 Good Friday peace deal.
But once the UK leaves the EU, the border - heavily policed during the Troubles in Northern Ireland - will become one of the EU's external borders.
Last June a majority of voters in Northern Ireland and Scotland voted to remain in the EU, but the UK Leave campaign won overall because so many in England backed Brexit.
"We want to have the Good Friday agreement not being put under risks, and we want land borders being as open as possible," Mr Juncker said.
A veteran European Commission politician, France's Michel Barnier, will be the EU's chief negotiator on Brexit, and he attended the Juncker-Kenny talks on Thursday.
The Commission and Irish government "will work closely together during the whole process of the Brexit negotiations," Mr Juncker said.
Mr Kenny said Dublin was very concerned by the implications of Brexit and wanted "the closest possible relationship between the UK and the EU".
"There should not be a return to a hard border and there won't be," AFP news agency quoted him as saying.