Mr Varadkar said the UK’s departure from the EU has “undermined” the Good Friday Agreement and it is damaging the relationship between Britain and Ireland.
Speaking on RTE Radio One’s Marian Finucane programme, the Irish Prime Minister said: “Brexit has undermined the Good Friday Agreement and it is fraying relationships between Britain and Ireland.
“Anything that pulls the two communities apart in Northern Ireland undermines the Good Friday Agreement and anything that pulls Britain and Ireland apart undermines that relationship.”
It comes days after Nobel peace prize winner and Ulster Unionist Lord Trimble accused Mr Varadkar’s government of “riding roughshod” over the 1998 agreement.
Lord Trimble said Brexit could leave Northern Ireland as part of an “effective EU protectorate” by the Brexit process.
Tensions are rising as Brexit talks are at a deadlock, with the UK and EU failing to reach a deal despite the deadline looming.
The UK and the bloc are at a stand off over the EU’s backstop proposal, which would keep Northern Ireland locked in to the customs union and single market if arrangements to prevent a hard border in Ireland are not made.
But Ireland’s Deputy Prime Minister said yesterday that he believes a Brexit deal could be made by the end of this month.
Speaking at a conference in Dublin, Simon Coveney said “a lot of progress” had been made in recent weeks.
Mr Coveney said the EU’s chief negotiator Michel Barnier has shown ”flexibility and imagination to overcome some of the political challenges that are clearly there”.
He said: “I think a deal can be done, but I think it’s important that the commitments that have been made are followed through on in full.
“If that happens, I think it’s possible to ensure that we get a withdrawal agreement that can be sold on both sides of the Irish Sea.
“I think it is possible to get a deal in November.”
On the Irish border, Mr Coveney added: “This border issue is complicated to resolve…but I think we’re very close to resolving it. I certainly hope we are.”