Leo Varadkar has admitted it would be "very difficult" to avoid a hard border in Ireland if there was a no-deal Brexit.
The Taoiseach's comments came amid continuing political chaos in the UK and huge uncertainty as to whether Prime Minister Theresa May can get her Brexit deal with the EU through parliament.
That deal would prevent a hard border in Ireland as all of the UK would stay in a form of customs union with the EU.
However, it is being opposed by Brexiteers in Mrs May's own Conservative party, as well as much of the Labour Party, putting it in serious doubt of being approved in the House of Commons.
There was relief in Government Buildings earlier this week when it emerged Mrs May's cabinet had approved the proposed draft withdrawal agreement with the EU.
However, within 24 hours there was a series of resignations by British ministers opposed to the deal, including Brexit secretary Dominic Raab.
Eurosceptic Tory MPs have stepped up efforts to remove Mrs May. A vote of no confidence in her leadership is possible as early as next week.
Last night, Mr Varadkar continued to express hope that the deal will be passed but said he appreciated that Mrs May will have "quite the battle" to get the deal through parliament.
The Government here has consistently said it will not accept a hard border, but Mr Varadkar last night conceded in a no-deal scenario "it would be very difficult to avoid a hard border".
He said Ireland would "no doubt" be asked to implement EU laws to protect the single market, and Britain would have to implement World Trade Organisation (WTO) rules.
"The only way we can avoid a hard border is by an agreement that covers customs and regulations. We have that now," he said.
He added that he doesn't see much room for renegotiating the deal, warning that such a move could see it "unravel".
"As reality kicks in," the Taoiseach said, there may be more MPs willing to support the deal as "the best possible outcome that can be achieved". He admitted Ireland is continuing to prepare for a no-deal Brexit.
"We have to be prudent," he said, but insisted he was "much more confident now that the worst case scenario won't arise".
"The truth is no country can be fully prepared for a no-deal Brexit," he said. "It would be an extremely chaotic situation and we might find ourselves after a few weeks of chaos signing up to an agreement much like the one we have now. People need to consider that."
Tanaiste Simon Coveney said that there were no contingency plans being prepared for a hard border, whether there was a deal or not.
He said that the way to avoid a hard border was to support the deal that had been agreed by the EU and the UK.
Mr Coveney warned coming to a solution that would maintain the soft border if Britain crashed out "won't be easy".
However, he refused to be drawn on how a hard border could be avoided.
"In the absence of that deal being approved, it would be difficult to put an alternative that prevents a hard border, but we will do that if necessary," he said.
Mrs May, who has appointed Stephen Barclay to replace Mr Raab, will take sole control of negotiations on EU withdrawal, with his role related to the domestic delivery of Brexit.
Meanwhile, high-profile Brexiteer Michael Gove offered Mrs May a lifeline by saying he has confidence in her and will stay in her cabinet.