Ireland cannot be asked to “compromise on something as fundamental as the peace process”, Irish Foreign Minister Simon Coveney has said.
He was speaking as Theresa May attempts to seek changes to her rejected withdrawal agreement.
However, he said Ireland could show more flexibility after a deal has been done.
On Friday, his government unveiled the major legislation it has prepared to manage a no-deal scenario.
It covered a wide range of emergency measures that will be enacted if the UK leaves the EU without a deal.
His comments come as the prime minister announced that MPs will have a final vote on the Brexit deal on 12 March.
Mrs May ruled out a parliamentary vote on the deal before the end of February.
Mr Coveney told Sky News said that while the EU stands firm on not changing the withdrawal agreement, it is trying to “provide reassurance and clarification for the British parliament to allow them to ratify this deal”.
The prime minister is trying to renegotiate the backstop – the insurance policy to prevent the return of physical checks on the border between Northern Ireland and the Republic of Ireland.
‘Placating Conservative group’
Mr Coveney said Brexit was “not just about Westminster”.
“If Britain wants a deal you can’t ask Ireland to compromise on something as fundamental as a peace process and relationships linked to the Good Friday Agreement in order to get a deal through,” he said.
Mr Coveney added that the government’s position was “about placating a group in the Conservative Party who are insisting on moving the prime minister away from her own policies”.
“The backstop was a British government construct as much as it was an EU and Irish government construct.
“This is about a shared responsibility,” he added.
He again reiterated the need for a guarantee to those in border counties that they will not face physical or security border infrastructure.
“Surely that not an unreasonable request,” he said.
The UK remains on course to leave the European Union on 29 March.
However, the government has repeatedly refused to rule out the possibility of the UK leaving without a formal deal, in the event that Mrs May cannot get MPs to approve the deal she negotiated with Brussels in time.
Mrs May is expected to hold talks with European Council president Donald Tusk and other key EU figures in Egypt later during a summit between leaders of EU and Arab league countries.
But Downing Street has played down hopes of a breakthrough on her Brexit deal being reached in Sharm el- Sheikh.
The summit is the first between leaders of EU and Arab league countries and will focus on tackling concerns over security and migration, and boosting trade.