Sinn Féin leader Gerry Adams says Brexit deal 'does not address key areas'
Sinn Féin has given a "cautious and qualified" welcome to the agreement on the Irish border post-Brexit.
Party president Gerry Adams said many questions remained without answer.
"Brexit is the greatest threat to the economies of this island in generations," he said in Dublin.
"Today's communique does not set the final deal on Brexit.
"The communique sets out broad principles. These have been assessed by the Irish government as sufficient progress to allow the Brexit process to move into the next phase of negotiations on trade.
"While the communique recognises the unique and special circumstances surrounding the issue of the Irish peace process, the Good Friday Agreement and the border, it does not address key areas of concern for many citizens - especially nationalists living in the north and citizens in the border region.
"The insistence by the British that Britain and the north must leave the customs union and the single market presents a real and live danger which cannot be understated.
"This also contradicts the British prime minister's claim that there will not be a hard economic border.
Mr Adams said he had concern at the suggestion Northern Ireland would no longer be subject the jurisdiction of the European Court of Justice.
He added: "While today's communique represents some progress there are many unanswered questions around key issues and the Irish government must remain focused and vigilant.
"Sinn Féin is also very mindful that this Brexit process is a work in progress.
"Our experience through years of agreements with Britain is that the devil is in the detail."
Earlier today the DUP welcomed the "substantial progress" achieved in the agreement between the UK and EU, but cautioned that much more work was needed on managing the border post-Brexit.
DUP leader Arlene Foster said her party worked with the British government into the early hours of Friday to secure changes to the original text it rejected on Monday.
Mrs Foster said Northern Ireland would now leave the single market and customs union and insisted there would be no border down the Irish sea, dividing Northern Ireland from the rest of the UK.
"There will be no so-called 'special status' for Northern Ireland as demanded by Sinn Féin," she said.
Mrs Foster added: "Northern Ireland will not be separated constitutionally, politically, economically or regulatory from the rest of the United Kingdom, and the joint UK-EU report at the conclusion of phase one makes clear that in all circumstances the United Kingdom will continue to ensure the same unfettered access for Northern Ireland's businesses to the whole of the UK internal market."