A Brexit "no deal" is now more likely than one with agreement, Taoiseach Leo Varadkar warned.
Speaking during the British-Irish Council summit in Guernsey on Friday, Mr Varadkar also said that efforts between the European Union and Britain to find a deal would be intensified and expressed hope that an "orderly Brexit" was still achievable.
The council brings together the UK and Irish governments with the Scottish and Welsh devolved administrations and British crown dependencies to discuss common issues.
During the summit, it also emerged that both Guernsey and Jersey are planning for the possibility of a Brexit without a deal.
“I think it’s more likely than it was a few months ago, but I still don’t think it’s likely,” said Mr Varadkar during a summit press conference.
"Ultimately, it's in the interests of Ireland; in the interests of the United Kingdom; in the interests of the European Union that we have an orderly Brexit and a new relationship that works for everyone.
“So, that’s what we are going to try and do over the next couple of months. We are going to intensify our efforts to come to a withdrawal agreement.”
Hard border
Scottish first minister Nicola Sturgeon said she was "acutely aware" of the Irish Government's priority to avoid a hard border, adding: "They have been a voice in this that has tried to bring reason and argue for an outcome that is in everybody's interests."
The idea of the UK remaining in the EU single market and customs union was still not off the table, she insisted, with no majority in the House of Commons or across the UK for a “hard Brexit”.
"The option that sees the UK remaining in the single market and the customs union wouldn't just be right in my mind for Scotland, and indeed the UK economic interests, but it would effectively resolve the Irish issues that we're been talking," said Ms Sturgeon.
The chief minister of Guernsey also said the island had to consider the possibility of a Brexit no-deal. “It is absolutely inevitable, sensible, wise and prudent that all administrations should be preparing for that, not necessarily with any expectation that will be the outcome,” Gavin St Pier said.
“But clearly, it is prudent government to ensure you have got that preparedness whilst clearly planning for a more favourable outcome as the Taoiseach said.”
Customs union
Referring to the Irish Border, Mr St Pier added: ‘The crown dependencies have a not dissimilar challenge to ensure that we have a customs union with the United Kingdom, that we don’t end up with a border running through the middle of the channel from here.”
Jersey's external affairs minister Ian Gorst said ensuring a common travel area and a customs unions between the Channel Islands and the UK was the "most important priority", while wanting to maintain a relationship with the EU. Asked about planning for a Brexit no-deal, he said: 'We are planning for all scenarios.'
However, British cabinet office minister David Lidington remained positive that a deal would be reached. There had "been some good progress on most aspects of the withdrawal agreement in the past few weeks," he said.
“There are certainly, most obviously with the Irish backstop, there are a couple of important outstanding issues that we need to work on intensively in the months to come.
“But I remain confident that a withdrawal agreement will be reached in the autumn. That is something that is so evidently all in the interests of all 28 countries involved.”