Sinn Féin has accused the DUP of showing a reckless disregard for the Good Friday Agreement after leader Arlene Foster claimed the peace deal was not sacrosanct.
Party leader Mary Lou McDonald insisted the 1998 accord between the British and Dublin governments must not become a bargaining chip in the Brexit negotiations.
She reacted angrily after Mrs Foster suggested the terms of the agreement could be altered in efforts to strike an EU exit deal.
"Today's comments by DUP leader Arlene Foster on the Good Friday Agreement are unacceptable and reveal a reckless disregard for the peace process, prosperity and progress," said Mrs McDonald.
Critics of Brexit have warned of its potential to undermine aspects of the treaty, including its provisions for cross-border co-operation and rights protections.
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The DUP campaigned against the Good Friday Agreement when it was resoundingly endorsed in referenda on both sides of the border in 1998.
Elements of the deal have been altered by subsequent political agreements, such as the 2006 St Andrews Agreement.
In an interview with the Daily Telegraph, Mrs Foster said: "It has been deeply frustrating to hear people who voted Remain and in Europe talk about Northern Ireland as though we can't touch the Belfast Agreement. Things evolve, even in the EU context.
DUP leader Arlene Foster addresses her comments on the Good Friday Agreement, where she said the deal was not a sacrosanct piece of legislation pic.twitter.com/lxYeLLEwaz
— RTÉ News (@rtenews) October 2, 2018
"There has been a lot of misinterpretation, holding it up as a sacrosanct piece of legislation."
In response, Mrs McDonald called on the Dublin government to make clear that the terms of the deal would be protected.
"It should be remembered that Arlene Foster left the UUP, which supported the Good Friday Agreement, to join the anti-agreement DUP," she added.
Arlene says that the Good Friday Agreement isn't 'sacrosanct'. Whether Arlene likes it or not, the people of Ireland voted for the agreement in huge numbers. Changes that were made at St Andrews have led to the problems we have today. There will be no more messing with the GFA.
— Colum Eastwood (@columeastwood) October 2, 2018
"It appears the DUP leader has learnt nothing over the past 15 years.
"Brexit is incompatible with the Good Friday Agreement. The actions of the DUP and their deal with the Tories is bad for our economy and undermines the rights of citizens."
The latest row between the DUP and Sinn Féin comes amid the ongoing political impasse in the north following the collapse of the powersharing institutions in early 2017.
"The Good Friday Agreement was endorsed by the vast majority of people north and south," said the Sinn Féin president.
"It is the people's agreement and not a chip to be bargained with as part of any Tory/DUP Brexit deal.
"The DUP should commit to the full implementation of the Good Friday, and other agreements, rather than seeking to undermine them.
"This would unlock the pathway to re-establishing the political institutions and safeguarding the interests of all the people in the north."
UUP leader Robin Swannn said Ms Foster’s comments on the Agreement were“strategically shortsighted”.
"The DUP may have been happy to corrupt the 1998 agreement for their owns ends at St Andrews, but I cannot believe the DUP Leader has been so careless as to throw it open in such a haphazard way which is of no benefit to unionism," he said.
“The reality is that the principle of consent is what binds us to the United Kingdom, it is the best settlement for unionists and should be sacrosanct. We should be looking to build on this principle and ultimately remove the changes made at St Andrews to finally do away with the sectarian politics which continues to plague us to this day.
Mr Swann also criticised Mary Lou McDonald, saying Sinn Féin were "complicit in destroying the partnership model of government established by the Belfast Agreement."
Tánaiste Simon Coveney branded Mrs Foster's comments "wrong".
He tweeted: "I have respect for Arlene, but she is wrong on this. GFA was voted for by overwhelming majority in NI & IRL, has helped to end violence + provided for the most prolonged period of peace+stability in NI's history. We will defend+ protect it through #Brexit."