Taoiseach (prime minister) Leo Varadkar said the future of the border between the Republic of Ireland and Northern Ireland must be clarified before Brexit talks can progress to the second stage.
The threat was issued during a joint press conference held by Mr Varadkar and president of the European Council Donald Tusk.
Mr Varadkar said: “I believe with the right engagement and political will we can reach an agreement on the way ahead.
“However I’m also prepared to stand firm with our partners if needs be if the UK offer falls short on any of those three issues including the Irish ones.”
Mr Tusk told Mr Varadkar the other members of the EU27 remained in total support of Dublin’s stance.

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He said: “The key to the UK’s future lies in some ways in Dublin, at least as long as Brexit negotiations continue.”
This is a developing story, more to follow…