The Irish Government will not stand for any backsliding on the deal struck over the issue of the border in the first phase of the Brexit negotiations, the country's Foreign Affairs Minister as said.
Tanaiste Simon Coveney said he hoped Britain would strike a deal on trade with the European Union in the next round of talks.
But he said it was difficult to see how Prime Minister Theresa May would secure a new arrangement and avoid the need to adopt a fall-back position of full alignment with the customs union and single market on the island of Ireland.
The comments were made in the Dail a day after Mr Coveney called on the UK Government to drop its red lines and tough talk on the future relationship with the EU.
Mr Coveney said there was no uncertainty over what had been agreed on the border.
"We intend on ensuring that that commitment is maintained," he said.
"We will not be backsliding."
Mr Coveney said he hoped both sides would be able to come to an agreement.
"I hope we can resolve these issues with a broad trade agreement," he said.
"But of course it is difficult to see how we can avoid using that fall-back position if the British Government is determined to pursue a strategy that results in them leaving the single market and leaving the customs union in an absolute way."
"The negotiations that were negotiated before Christmas are very clear about the issue of the border, and indeed in many other areas," he said.
"We want to make sure there is no pullback from those commitments in the context of the broader negotiations as they move ahead."
The European Union is in the process of finalising its negotiating guidelines on the withdrawal of the UK from the EU.
They are expected to be published the end of March.