Ireland's Foreign Affairs minister said a no-deal Brexit would have to become "an exercise in damage limitation".
Speaking in the Irish parliament, Simon Coveney said: "It would be impossible in a no-deal scenario to maintain the current seamless arrangements between the EU and UK across a full range of sectors, which is currently facilitated by our common EU membership."
Mr Coveney said the EU would continue to seek to be as helpful as possible but that the Withdrawal Agreement was not open for renegotiation.
"It acts as an insurance policy, to ensure that there is no hard border on this island following Brexit. It is essential."
Although the Withdrawal Agreement is not open for renegotiation, Mr Coveney said if the UK chose to shift its red lines on leaving the customs union and the single market, and opt for a more ambitious relationship "beyond a basic free trade agreement, the EU would be happy to evolve its position".
Mr Coveney said: "While our focus remains on securing an orderly and agreed Brexit, given the uncertainty in London, and the increased risks of a no-deal Brexit, the Government will continue to intensify our preparations for such an outcome.
He added that Ireland's number one protection from Brexit was the country's membership of the EU.
In a phone conversation with Secretary of State Karen Bradley, Sinn Féin's Deputy leader expressed her concerns about the unfolding events in Westminster.
Michelle O’Neill said: “I had a frank discussion with the British Secretary of State and I told her that her government is clearly still not listening to fears of the public who are aghast at the pantomime currently playing out in the Westminster parliament.
“With each passing day, our business community, our farmers, our community and voluntary sector are growing more concerned at where this shambles will ultimately end up. And it is they who will pay the price of a no-deal crash Brexit."
“Unfortunately that is where we are likely to end up if Karen Bradley’s government pursues a solution by attempting to placate and appease the DUP and the hard Brexiteers.
She added: “Those people are clearly not concerned about the impact of their reckless actions on our economy and our communities."
Michelle O'Neill said it's important that the Dublin Government and the EU27 "stand firm" on their position, stating that "there can be no agreement without a backstop".