Irish opposition leader Micheal Martin has criticised the Democratic Unionists over their reaction to the Brexit deal reached between the UK and the EU.
DUP leader Arlene Foster voiced concern about the deal, while East Antrim MP Sammy Wilson said his party will not vote for it.
Some Conservative MPs have also criticised the deal, claiming it would keep the UK under EU control.
Mr Martin said the matter "deserves better than that".
"I was a bit dismayed to see people coming out very early - Sammy Wilson from the DUP, for example - even before they had read anything to do with the text, proclaiming they were going to oppose it, and people from the hard Brexiteer group as well," he said.
"I think the issue deserves better than that, and I would hope that the other parties in Britain would stand back and look at this in detail and come to a considered position on the agreement which has been reached between the European Union and the United Kingdom."
The Fianna Fail leader said relations between the Republic of Ireland and Northern Ireland are at their lowest in 20 years and blamed the Conservative Government at Westminster and the Fine Gael administration in Dublin for changing "the overall dynamic".
"Where the Major, Blair and Brown governments had shown a deep commitment to Northern Ireland's long-term progress, there was an apparent impatience in the Cameron government that they still had to spend time on the issue," he said.
"In fact David Cameron's approach was that Northern Ireland had to 'stand on its own two feet' rather than expect London to help overcome every problem.
"The change of government in Dublin also marked a new approach. Set-piece meetings continued but there was a clear disengagement and an expectation that it was time to just let the DUP and Sinn Fein get on with business."
Speaking to the media at an Irish Association conference at Queen's University Belfast, Mr Martin said:
"I welcome the fact that the European Union and the United Kingdom, it seems, have agreed on a text for the withdrawal part of the agreement.
"The devil is in the detail and that is something we have got to keep an eye on, not just today but in the coming years. Brexit is going to be a long journey, this is just the withdrawal agreement.
"What's key for me is Brexit is not good for Ireland, it's not good for Britain, so we have got to aim for the softest Brexit possible.
"A no-deal scenario would be Armageddon, it would be ruinous for Britain."
Speaking at the same event Ulster Unionist Steve Aiken also commented on deteriorating relations both north/south and east/west.
He said: "The DUP told us they were holding the Conservative Party to account. Look what they have done, they have undermined the union, they have helped destroy devolution in Northern Ireland, the DUP has been an absolute disaster.
"It has been a disaster for Northern Ireland, it has been a disaster for unionism, and I think members of the DUP need to very clearly reflect on where they have got themselves in this position."