The Taoiseach says it is not up to Ireland to design a solution to Britain's EU departure
Former Northern Ireland First Minister David Trimble has said Taoiseach Leo Varadkar should "go away and calm down" and reconsider his comments on an Irish border.
Mr Varadkar says it is not up to Ireland to re-design the new border after Brexit because Brexit is not Ireland's idea.
In his strongest-worded comments yet, Mr Varadkar said leaving the European Union was not an Irish policy and it was not up to Ireland to design the solution to Britain's departure.
He said Ireland will not help to design a border it does not want.
"It's as simple as this: between Ireland and Northern Ireland there is a political border. Northern Ireland is part of the United Kingdom, Ireland is a sovereign, independent state.
"But currently there is no economic border and there hasn't been an economic border since 1992 - and as far as this Government is concerned there shouldn't be an economic border, we don't want one.
"It's the United Kingdom, it's Britain that has decided to leave; and if they want to put forward solutions - smart solutions, technological solutions, borders of the future and all of that - that's up to them.
"We're not going to be doing that work for them, because we don't think there should be an economic border at all".
"We're not going to be helping them to design some sort of border that we don't believe should exist in the first place.
"So let them put forward their proposals as to how they think a border should operate, and then we'll ask them if they really think this is such a good idea because I think it'll have a very severe impact on their economy if they decide to go down that route".
Mr Trimble says Ireland is toying with the Good Friday Agreement if it proposes any plan like that.
"I do have to say to the new Irish prime minister and new Irish foreign minister they should go away, calm down and look carefully at that agreement that we negotiated.
"They need to go back to that, and to think carefully about their obligation to abide by that agreement - and not to be seen to try to undermine it".
"By raising this suggestion then this will do enormous damage to the relationships between Belfast and Dublin, which have been quite cordial since the agreement.
"But if Dublin starts to undermine the essential, constitutional basis which is the heart of that agreement then they are doing themselves a grave disservice".
It comes after British complaints that Ireland was seeking a sea border between the two islands after Brexit takes effect.
Foreign Affairs Minister Simon Coveney has called on the EU to move Ireland's border into the Irish Sea.
The British Chancellor of the Exchequer, Philip Hammond, said placing the border in the Irish Sea was unacceptable.
"The answer to how to deliver that cannot be to create a border between Northern Ireland and Great Britain.
"That would not be a solution that was acceptable to us, or indeed to the people of Northern Ireland."
Members of the DUP have also come out strongly against the idea.
Fianna Fáil spokesperson on Brexit, Stephen Donnelly, has said that any border with Northern Ireland must be avoided in the interests of all of the people living on the island of Ireland.
"It is important that we have an honest conversation with our UK neighbours, and despite coming late to the table on this issue, I am relieved that the Government now appears willing to start that conversation.
"Fianna Fáil believes that the welfare of the people of Northern Ireland must be front and centre of any Brexit discussions.
"Any border around the six counties - either physical or electronic - will be to the determinant to the people of Northern Ireland and must be avoided at all costs."
In response to Mr Varadkar's comments, a spokesman for Britain's Department for Exiting the EU said: "Finding a solution to the border between Northern Ireland and the Republic of Ireland is a top priority, which we want to address early in the negotiations.
"We are pleased to have had constructive discussions with the European Commission on this already.
"As we have always been clear, our guiding principle will be to ensure that - as we leave the EU - no new barriers to living and doing business within the UK are created.
"We aim to have as frictionless a border as possible between Northern Ireland and the Republic of Ireland, and we welcome the European Council's recognition that flexible and creative solutions will be required.
"It is our priority to deliver a practical solution, that recognises the unique social, political and economic circumstances of the border."
Additional reporting: Michael Staines and Jack Quann