Efforts to avoid a hard border may hit real difficulties if the UK changes its customs rules after a no-deal Brexit, the taoiseach (Irish PM) has said.
Leo Varadkar explained that if the UK leaves the EU without a deal, it would still be aligned to EU customs and regulations as things currently stand.
He said problems would only arise if the UK decided to make changes.
The taoiseach added the UK and EU must continue to have customs and regulatory alignment to avoid a hard Irish border.
"It is all very well to say that nobody wants a hard border, we don't... but if you don't have alignment on customs and regulations then you get into real difficulties," Mr Varadkar said.
The Irish government is now prioritising planning for a no-deal Brexit.
However, the taoiseach insisted ministers were not preparing for a hard border nor planning to introduce any sort of physical infrastructure between Northern Ireland and the Republic of Ireland.
He said the best way to avoid a hard border is to implement the draft EU Withdrawal deal that was agreed with UK Prime Minister Theresa May.
Earlier, the tánaiste (Irish Deputy PM) said the Irish border was not addressed in his government's contingency plan in the event of a no-deal Brexit because the backstop is the only solution.
Simon Coveney told Irish national broadcaster RTÉ: "For us to be giving signals that there's any other way this could be solved would be foolish."