Northern Ireland must continue to apply EU single market and customs union rules to avoid a hard border, Irish Prime Minister Leo Varadkar has said.
The Taoiseach said the UK or Northern Ireland would not necessarily have to remain members of either as a "bespoke" arrangement could be reached.
James Brokenshire, the Northern Ireland secretary, said the UK Government is ready to be "pragmatic" in acquiring a solution to the "unique circumstances" facing the nation, regarding its currently open border with the EU.
Mr Varadkar's suggestion came after a leaked European Commission document said the Republic is making a big push for firm reassurance on the border question before the crucial EU summit in December when Theresa May is hoping to get the go-ahead for trade talks to begin.
The paper, obtained by the Daily Telegraph, said to preserve the Good Friday Agreement peace deal the Brexit deal must respect "the integrity of the internal market and the customs union".
Northern Ireland's border is one of the three key initial Brexit issues, along with expat citizens' rights and the divorce bill.
EU leaders have said "sufficient progress" must be made on all three topics before the remaining 27 leaders will give the go-ahead for trade talks.
Mr Varadkar told the British-Irish Council summit in Jersey he was "loath to comment in too much detail on papers that have been leaked to the media".
He added: "When it comes to the border between Ireland and Northern Ireland, what we have all agreed to is that there shouldn't be a hard border, there should be no physical infrastructure along that border and that there should be no return to the borders of the past.
"It is our view, and has been our view for a very long time, that the only way that can be achieved is if the United Kingdom as a whole, or Northern Ireland, continues to apply the rules of the customs union and the single market.
"That doesn't mean that they have to be members of it, but it would mean continuing to apply the rules of the single market and the customs union.
"That's the position that we hold and the best way to achieve our common objectives."
Mr Brokenshire said Mrs May had been clear the UK will no longer be a member of the single market and the customs union when Britain leaves the EU in March 2019.
Mr Varadkar added: "We are looking for a bespoke solution here that achieves the objective that we all share, which is no hard border, no return to the borders of the past and no physical infrastructure along that border."
During another speech later on Friday, the first to his party since becoming Taoiseach, he vowed to safeguard the rights of border communities.
He said he was certain Ireland will remain at the heart of Europe.