Anyone believing the EU's solidarity with Ireland may diminish is in for a "nasty surprise", the taoiseach (Irish prime minister) has said.
Leo Varadkar made the comments during the All-Island Civic Dialogue conference in Dublin Castle.
The event aims to discuss the implications of the UK's vote to leave the European Union on 29 March.
Mr Vardkar added: "Ireland's concerns have become the European Union's concerns".
'Redline' for Ireland and EU
On Friday, the taoiseach said Ireland had received "remarkable solidarity" from the EU since the UK voted to leave.
"Despite many attempts to bilateralise issues, or to divide the 27, the solidarity has been strong and resolute, and those who believe it will break at the last moment are in for a nasty surprise," he added.
He said Ireland's "insistence on the legally binding and operable solution to avoid a hard border has become an EU redline as well".
The backstop is an insurance policy - contained within the withdrawal agreement - which aims to prevent a hard border between Northern Ireland and the Republic of Ireland if no other solution can be found through a wider trade deal with the EU.
Many have opposed the backstop, claiming there are alternative ways to resolve the border issue.
The tánaiste (Irish deputy prime minister) said on Wednesday that those claiming the backstop was not needed were making "farcical arguments".
Mr Varadkar said the withdrawal agreement was "not a perfect deal" but that it was "fair".
"I had firmly hoped that the UK would ratify the agreement, so that we can move forward," he added.
The taoiseach said he had been "assured in the strongest terms" by Presidents of the EU Institutions that the EU "stands by the withdrawal agreement, including the protocol on Ireland and the backstop".
He said "the commitment on the border has to be watertight" and that nobody "has suggested credible alternative arrangements" in the two years since the referendum vote.
In relation to the prospect of a no-deal Brexit, Mr Varadkar said planning had intensified.
"It's no longer contingency planning, it's planning for a very real outcome," he said.
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