Gerry Adams has said Ireland should prevent Brexit talks on links between Britain and the EU.
The Sinn Fein leader claimed Britain’s plans so far were unworkable and unrealistic.
The EU has decided that discussions on its future relationship with Britain, including trade, can only start once sufficient agreement is reached on issues like the Irish border.
In the latest round of negotiations genuine progress was made on issues like maintaining freedom of movement for citizens of the two countries between the UK and Ireland, Europe’s chief Brexit negotiator Michel Barnier said – but he added no decisive breakthrough had been made.
Mr Adams said: “The fact that no definitive progress has been made in these talks is evidence that the British Brexit plans are unworkable and unrealistic.
“The Irish government should insist that the negotiations are not ready to move to the next stage.”
The UK’s only land frontier with an EU state post-Brexit will run between Northern Ireland and the Republic and citizens of both countries fear they could be particularly disadvantaged. Irish citizens living in Great Britain have also raised concerns.