Brexit is "fraying" the relationship between the UK and Ireland and putting peace in Northern Ireland at risk, Irish premier Leo Varadkar has said.
The Taoiseach said the Good Friday Agreement was being "undermined" by fractious relations between the two countries over how the Northern Irish border should be managed once Britain leaves the EU.
It comes just a day after Theresa May's de facto deputy, David Lidington, travelled to Dublin to hold talks with his Irish counterpart, Simon Coveney, in a bid to improve relations between the two governments.
But speaking within hours of the visit, Mr Varadkar described the relationship between the two countries as "fraying".
He told Irish broadcaster RTE: "Brexit has undermined the Good Friday Agreement and is fraying the relationship between Britain and Ireland.
"Anything that pulls the communities apart in Northern Ireland undermines the Good Friday Agreement, and anything that pulls Britain and Ireland apart undermines that relationship."
The warning comes despite Mr Coveney having claimed a deal between the UK and the EU was "very close".
Mr Varadkar was speaking hours after another senior Irish politician also claimed the return to a hard border would threaten peace in Northern Ireland.
Senator Neale Richmond, who chairs the Brexit committee in the Irish parliament's upper house, told Radio 4's Today programme: "When we talk about political goodwill I think it's very important...why the Irish government and why the European Commission is so firm on an Irish-specific backstop is the preservation of peace.
"It's the 20-year-old fragile Good Friday Agreement peace, something that the Irish government and indeed the British government is a co-guarantor of, and we must work to ensure that there is no hard border, customs or otherwise, on the island of Ireland, as that is a threat to that Good Friday Agreement. Let's focus on that first and foremost."
Earlier in the week, former unionist leader David Trimble accused Mr Varadkar's government of "riding roughshod" over the Good Friday Agreement.
Lord Trimble, who was closely involved in the talks that led to the peace treaty, voiced fears that Brexit could lead to Northern Ireland being held in an "effective EU protectorate".
The UK and EU have so far been unable to agree on the customs backstop that will govern how the Northern Irish border should be managed in the event that there is no trade deal to maintain an open border.
The UK is pushing for a backstop that would see the whole UK remain in the customs union temporarily, but the EU also wants the option of only Northern Ireland staying in the bloc.
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