European Commission President Jean-Claude Juncker has reportedly told UK Prime Minister Theresa May in a telephone call that she will have to sign up to a permanent customs union if she wants the EU to revisit the backstop.
Mr Juncker is said to have told Ms May she would have to significantly change her red line position on remaining in the customs union if she wants the EU to negotiate on the backstop.
The Irish backstop is an insurance policy in the Brexit Withdrawal Agreement which ensures against a hard border returning to the island of Ireland.
Details of the telephone conversation came as European Commission Vice-President Frans Timmermans said there was “no way” he “could live in a situation” in which the EU “throw Ireland under the bus”.
“As far as the European Commission is concerned, the backstop is an essential element for showing to Ireland and to the rest of Europe that we are in this together,” Mr Timmermans told the Guardian newspaper.
“Mind you, a backstop is called a backstop because it doesn’t have a time limit. If it has a time limit it is no longer a backstop, so that backstop for the European Union is very important. And there can be no uncertainty about that,” he added.
Meanwhile, hundreds of protesters have warned UK Prime Minister Theresa May that a hard Irish border risks destroying Northern Ireland's hard-won peace.
A mock checkpoint manned by actors dressed as soldiers and customs officers was constructed close to the frontier in Co Down on Saturday.
Machine gun-toting soldiers' "towers" were camouflaged in green and black and concrete blocks were craned into place across the road as a backdrop for a string of angry speeches by anti-Brexit campaigners from across the island.
If the UK leaves Europe without a deal, the free flow of goods could be disrupted by the creation of a hard frontier on the island, the European Commission has said.
Demonstrator Tom Murray, from Co Donegal, said it is Theresa May's responsibility to sort out the issue.
He said: "Ireland will not be made to suffer the folly of the Tory party.
"We are the ones who will be suffering for the mistakes made in Westminster.
"We will not accept this border, we demand that London sort out the problem that they created."
It is more than 20 years since the 1998 Good Friday Agreement which largely ended decades of violence.
Mr Murray added: "All the peace and prosperity that we have enjoyed will be destroyed by a hard border.
"Communities could be dragged back into the old days of living in the shadow of someone else's border.
"We are the people who will suffer the most."
Security towers manned by the British Army in the hilly and remote area near the city of Newry were decommissioned in 2003 as it ended conflict-era operations in Northern Ireland in support of the police.
The Irish and British governments have said they want to avoid a hard border after Brexit, and multiple sources have said Britain's withdrawal from the EU should not prompt a return to violence.
Some security sources have argued that if customs checks are put in place, police will be required to protect them and that could leave officers at risk from dissident republicans.
The Police Service of Northern Ireland has received extra resources for Brexit but have officially envisaged light-touch, community-style policing.
Foreign Affairs Minister Simon Coveney this week said it would be difficult to avoid installing new infrastructure following a no-deal Brexit.
Meanwhile, the UK must satisfy their Good Friday obligations to prevent the return of a hard border in the North of Ireland, according to Minister of State for European Affairs Helen McEntee.
Ms McEntee, speaking on BBC radio 4’s ‘Today’ programme, said that the Good Friday Agreement is more important than Brexit to Ireland.
According to the Fine Gael politician, there seems to be an attitude that it is Ireland’s responsibility to compromise during Brexit negotiations but that because Ireland didn’t vote in the Brexit referendum, it is the duty of the UK to obey their international peace treaty obligations as outlined in the Good Friday Agreement.
"We are protecting a peace process. There is an obligation on the UK to ensure that the peace process, the Good Friday Agreement, is protected,” she said.
“I think now, for some reason, the onus by the UK has been shifted back on Ireland. That we should compromise, that we are the ones that are trying to be awkward or difficult. We did not vote for Brexit. We don’t believe in it. We absolutely respect that it was a democratic decision, of course we do.
“We absolutely expect that the UK will fulfil its commitment, and will live up to its obligations because Brexit, or no Brexit, the UK Government is a co-guarantor of what is an international peace treaty."
Ms McEntee said that the only plausible preventative action for a hard border now is a backstop written into the UK’s withdrawal agreement.
While she said that the backstop is something the Irish government “never want to have to use”, the UK red line and lack of alternative solutions to the problems they pose, makes the backstop’s inclusion in the agreement “absolutely necessary.”
"It is because of those red lines that a backstop is absolutely necessary," she said.
“We don’t want to use the backstop. We’ve spent 18 month negotiating something we don’t ever want to have to use.
“For those Brexiteers, or others, who say that the backstop is not necessary, that we can avoid a hard border without it, I would ask them how they expect to do that because they are yet to come up with another solution.
“We are not asking you to change your red lines but we are asking you to respect that you have an obligation to an international peace treaty that you signed long before Brexit took place and for us the Good Friday agreement is much more important than Brexit.”
Ms McEntee said that Ireland has been continuously guaranteed the prevention of a return to a hard border throughout the Brexit process and that it is integral to the Good Friday agreement that their commitment is upheld.
“This is not just from an Irish point of view. There is an obligation on the UK to ensure that the peace process, the Good Friday Agreement, is protected. Any suggestion that they can walk away from that, we simply won’t accept.
“We have been very clear on this throughout the entire process. We are not planning for the reintroduction of a border. This is not an Irish policy, this is not something that we’ve voted on and certainly this is a commitment that was given time and time again.
“The UK government have given a commitment that we must protect the peace process and I think that must be something that people didn’t think about when they voted to leave the European Union but also to ensure that we never return to a border on this island.
“Integral to protecting that peace treaty is ensuring that we never return to any kind of borders that we saw in the past”.
With additional reporting from the Press Association
After spending the past two months denying there was any contingency planning for policing the Border in the event of a hard Brexit, Taoiseach Leo Varadkar yesterday performed an about-face and speculated on gardaí and troops being deployed there.
She describes him as one of her "early-morning skinny latte set", so she felt comfortable giving him a knowing grimace. "They're an oddball lot - most of my generation would never vote for them,'' she said.
With a mere 67 days to Brexit, the host of Claire Byrne Live (RTÉ1) promised us that last Monday night's show would provide "everything you need to know, from car insurance to food costs, medical expenses, flights and border controls".