The President of the European Council has said that EU will not accept any proposal on the border without Ireland’s agreement.
Donald Tusk was speaking following a meeting with the Taoiseach in Dublin this afternoon.
Addressing the press following the meeting, he reiterated that the EU is "fully behind" Ireland in its insistence that there can be no return to a hard border.
He said the UK decision to leave the EU has created uncertainty for millions of people around Europe – adding “perhaps nowhere is this clearer than here.”
He pledged to consult with the Taoiseach before agreeing to any UK offer on the border:
"Let me say very clearly," he said. "If the UK offer is unacceptable for Ireland, it will also be unacceptable for the EU.
“I realise that for some British politicians this may be hard to understand but such is the logic behind the fact that Ireland is an EU member while the UK is leaving.
"This is why the key to the UK’s future lies - in some ways - in Dublin, at least as long as Brexit negotiations continue."
Negotiators on both sides are facing in to a busy weekend as efforts continue to find a solution that would avoid a return to a hard border before Monday.
European leaders will vote on whether to allow Brexit talks to proceed to phase two at the upcoming European Council summit – however Mr Tusk noted that he had given the British Prime Minister Theresa a “final deadline” of Monday to come forward with a “final offer” on the border.
Mrs May will have the opportunity to table the offer when she meets with European Commission president Jean-Claude Juncker on Monday.
If progress is agreed, EU leaders will then sanction the second phase of Brexit talks at the summit on December 14th and 15th.
Speaking following the meeting, The Taoiseach said the British government must produce "credible, concrete solutions" to bring the impasse to an end.
He warned that the proposals must be in place before the talks are allowed to move on to the future trading relationship between the UK and the EU.
“The best and most obvious solution would be for the United Kingdom to remain in the Customs Union and the Single Market,” he said.
“But as the British Government has ruled that option out, it must offer credible, concrete and workable solutions that guarantee that there will be no hard border whatever the outcome of the negotiations and whatever the future relationship between the EU and the UK is.”
He said he believed an agreement could be reached with "the right engagement and the necessary political will."
He warned however that he is, "also prepared to stand firm with our partners if need be if the offer falls short on any of the three issues, including on the Irish ones."
“In two weeks time, Donald will chair a crucial meeting of the 27 EU leaders at which we will decide formally whether or not the sufficient progress test has been met and that will be a critical decision point,” he said.
“There has been some good progress in relation to the UK financial settlement and also EU citizen rights.
“These issues are crucial for all EU member states including of course Ireland.”
Good Friday Agreement
Mr Tusk said the border had become a “symbol of cooperation” over the years and insisted that Europe, “cannot allow Brexit to destroy the achievement of the Good Friday Agreement.”
He admitted that “agreement on every detail” will not be possible before the conclusion of the first phase of talks – noting that the nuts and bolts of the final outcome will be linked to the future trading relationship between the EU and the UK.
“It was the UK that started Brexit and now it is their responsibility to propose a credible commitment to do what is necessary to avoid a hard border,” he said.
He said Ireland has the EU's full backing in its insistence that there can be no return to a hard border:
"I came to Dublin to reassure the Taoiseach and all the Irish people that the EU is fully behind you in your request that there should be no hard border," he said.
"The Irish request is the EU's request."
Mr Tusk’s comments come as a new Westminster report claimed that a hard border is 'inevitable' after Brexit.
A committee of British MPs warned pulling the UK out of the single market and the customs union would make it impossible to achieve a "frictionless" border in Ireland.
Both Ireland and the EU have suggested the UK should remain within both agreements - a suggestion rejected out-of-hand by the British Government.
Meanwhile, the DUP has warned that it will not accept any deal that keeps Northern Ireland within the arrangements after Britain leaves.
The party has threatened to withdraw from the 'confidence and supply' arrangement that is propping up the British Government if any solution is put forward that barriers, "real or perceived" between the North and Britain.
The party's arrangement with the Conservatives has seen them voting as one on major legislation including the Queen's Speech, the Budget and Brexit.
However, the agreement does not cover the precise outcome of the EU divorce deal.
There has been some speculation that the British Government was considering some form of "regulatory convergence" between the North and the Republic that would break the deadlock, however DUP officials have suggested they view the plan as tantamount to keeping Northern Ireland within the customs union - thus creating a new unofficial border between Northern Ireland and the UK.
They have insisted this would be unacceptable, with one senior official claiming it could prove "deeply destabilising" to the confidence and supply agreement with the Conservatives.
Green versus orange
This morning, the Tánaiste Simon Coveney said the border debate cannot be allowed to become a ‘green versus orange’ issue.
He confirmed that behind-the-scenes conversations were being held with the DUP, however he warned that one political party cannot be allowed to have a monopoly over what happens to the border:
“I have tried – and I continue to try – to avoid this debate becoming a green versus orange issue in Northern Ireland, although it is very hard to prevent that, given some of the language that we have heard,” he said.
“Our approach here is to listen to everybody.
“No one party has a monopoly in Northern Ireland in the context of what is acceptable and what is not.”
He said negotiators will have to find a solution that is the right approach for the island of Ireland:
"Don’t forget that Northern Ireland did not vote to leave the European Union," he said.
“So there are broad and different views in Northern Ireland in terms of how we deal with this and we are listening to all of those views rather than just one party.”
He said the EU fully supports the Irish position, adding that the government will not need to flex its muscles on the issue:
“I don’t think there will be any need for a veto,” he said.
“This will be a European decision in terms of the EU task force.
“Either we can make sufficient progress on the three issues or else we are going to have a difficulty, at this point in time, moving on to phase two.
“We don’t want Ireland to be the problem here but at the same time we don’t want to move on to phase two and avoid the hard questions.”
Negotiators on both sides will be meeting across the weekend to try and hammer out an acceptable proposal that would allow talks to move forward.