THE European Union's chief Brexit negotiator has said that he will not sign any agreement with the UK government "unless we are satisified with the solution found for Ireland".
Michel Barnier made the remarks as he prepares to arrive in Ireland today for a two-day visit.
He said there will need to be "substantial progress" on the border issue by the next major meeting of EU leaders.
They are due to assess progress on the border issue at a summit in June.
Last week the Brexit Secretary David Davis suggested the EU was trying to create an "artificial deadline" in June as a negotiating tactic.
The Brexit secretary also dismissed reports that the European Commission has completely rejected the UK's plans for avoiding customs checks at the Irish border when the UK leaves the customs union.
October is the presumed deadline for a withdrawal agreement which will give the UK a smooth exit path from the EU.
In March, EU leaders agreed to a 21-month Brexit transition period between March 2019 - when the UK officially leaves - and the end of 2020.
Mr Barnier will address the fourth plenary session of the Irish government's all-island civic dialogue on Brexit, which takes place in Dundalk today.
The EU's chief negotiator is also set to cross the border to hear from business and lobby groups about the potential impact of Brexit.
Mr Barnier will host a round-table discussion in Newry today and has a similar engagement in Derry on Tuesday.
The former EU regional policy commissioner last visited Northern Ireland in 2000, but in his current role travelled to the border in Co Louth last May.
Writing in The Sunday Independent, Mr Barnier vowed to prevent the return of a border in Ireland and defend north-south cooperation and the Good Friday Agreement.
He said the EU's proposal of a 'backstop' option - in which Northern Ireland would remain aligned with the single market and customs union - would "apply unless and until another solution is found".
He wrote: "If the UK has a different idea, I am happy to look at it, but so far we have not received any workable solutions.
"Let me be crystal clear.....we will not sign any agreement with the UK unless we - together with the Irish government - are satisfied with the solution found for Ireland."
The Republic's foreign minister and Tánaiste Simon Coveney said: "We look forward to welcoming Michel Barnier to Dundalk and him updating attendees on the state of play in the negotiations.
"Mr Barnier and his team have demonstrated a keen understanding of the unique circumstances of the island of Ireland and they have Ireland's full support. We look forward to continued close cooperation with the taskforce."
