The EU's chief negotiator says that in the event of a no-deal Brexit, the EU's goal is to protect peace in Ireland and the single market.
Speaking during a visit to Dublin on Monday, Michel Barnier said the EU will stand fully behind Ireland, and the EU's 27 member states would remain fully united.
"If the UK were to leave the EU without a deal we would not discuss anything with the UK until there is an agreement for Ireland and Northern Ireland as well as for citizens' rights and the financial settlement," Mr Barnier said.
"You have our full support and, I have said before, the backstop is currently the only solution we have found to maintain the status quo on the island of Ireland."
Mr Barnier expressed confidence a solution would be found on how to protect the Good Friday Agreement all-Ireland structures as well as the integrity of the single market.
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"There have been intensive discussions between our teams over the past (few) weeks," he said.
"Our goal is to protect the Good Friday Agreement, peace on this island and the integrity of the single market.
"It is not an easy task but I am confident we will find operational solutions.
"One thing is for certain, whatever happens, the EU will stand fully behind Ireland."
He added that future work on the customs union could be done extremely quickly.
Mr Barnier also expressed hope that Conservative and Labour talks in London on a Brexit compromise would reach a "positive outcome", and that Britain's parliamentary process must be respected.
"We can be much more ambitious with our future relationship, and the political declaration provides a range of outcomes including a customs union, we are ready to make this clear if it helps," he said.
This was the fifth time Mr Barnier has visited Ireland in his current capacity.
Taoiseach Leo Varadkar expressed confidence that the EU27 would reach agreement at Wednesday's European Council meeting of leaders.
He reiterated that, although he wishes to see a deal ratified, contingency planning for a no-deal Brexit has intensified in Ireland, and that Ireland would be open to an extension.
Mr Varadkar added: "A no-deal Brexit would be damaging for everyone. For the United Kingdom, Ireland and the European Union.
"We also exchanged views on the length of an extension and I look forward to discussing this further with my EU counterparts at the EU Council.
"There will, of course, be different views, but I am confident we will reach agreement.
"However given the ongoing uncertainty we need to continue our preparations for a no-deal and that is exactly what we are doing.
"We also discussed in the case of a no-deal how best to meet our shared objectives, of protecting the Good Friday Agreement on which our peace is founded and also protecting the integrity of the Single Market and the Customs Union."
He added: "Should no deal arise, it will be a shared challenge."
