Irish Taoiseach Leo Varadkar has been accused of “poor manners” by a DUP MP for failing to follow protocol ahead of a visit to Northern Ireland.
Mr Varadkar headed north with EU chief negotiator Michel Barnier who was accused by DUP party leader Arlene Foster of not understanding unionist culture.
Mr Varadkar and Michel Barnier had earlier met in Dundalk on Monday morning at a conference focused on Brexit.
The two largest parties in Northern Ireland, Sinn Fein and the DUP, are on opposing sides over the EU divorce.
Sinn Fein has called for a new referendum on Irish unity within five years amid nationalist hopes the exit could inspire greater support for a united Ireland.
Following his appearance at the conference, Mr Varadkar travelled to Northern Ireland, in a move described by the DUP as “outside of normal protocol”.
MP Jeffrey Donaldson said: “Leo Varadkar’s visit is another demonstration of the poor manners and disrespect which appears to be the Irish Government’s Brexit strategy.
“Having told unionists just over a month ago that he recognised statements and actions by the Irish government were unhelpful or intrusive, he follows this up with a visit which no local representative is informed about and none of the other normal protocol is followed.
“It is increasingly apparent that the Irish government does not seem to care about securing a sensible and pragmatic outcome from Brexit which can work for both Northern Ireland and the Republic.
“Their preferred approach is to use Brexit in whatever way possible to undermine Northern Ireland and particularly its constitutional position.”
But Mr Varadkar said he has “no hidden agenda”, adding that he was resolutely committed to protecting the peace process across Ireland.
He said: “We don’t want things going backwards.
“We have to acknowledge that the continued absence of functioning political institutions in Northern Ireland is, at least partly, a consequence of concerns about, and different positions on, Brexit.”
He acknowledged some unionists were worried that Brexit could be used to undermine Northern Ireland’s union with Britain.
He said: “I want to repeat that we have no hidden agenda.
“Our agenda is fully transparent - it is respect for the primacy of the Good Friday Agreement and everything it represents for the people of these islands.
“That includes the principle of consent, peaceful politics, democratic institutions, reconciliation and co-operation.”
Mr Varadkar added: “I am determined to work with the British Government, with the political parties in Northern Ireland, with the unionist and nationalist communities to chart a way ahead.
“We want to see all parts of the Agreement operating and I also want to see the great strides that we have made on North/South co-operation continue and grow in the years ahead.”
Mr Donaldson’s comments cane after DUP leader Mrs Foster said Mr Barnier did not understand unionist culture.
She told the BBC: “He’s hearing a very strong message from the Republic of Ireland’s government, he’s hearing it from Sinn Fein.
“We have tried to get him to understand the unionist position for the people of Northern Ireland, but he hasn’t really responded to that and I’m disappointed about that.
In response, Mr Barnier said on Monday morning: “My door is open.”
Mrs Foster also accused the EU of aggression, telling the broadcaster: “Some of the utterances from the European Union... there’s an article in the Irish Independent today which is very aggressive in its tone.
“There are two jurisdictions on the island of Ireland. We are part of the United Kingdom. They have to respect that constitutional reality.”
Asked about the tensions when he arrived in Newry, County Down to meet business leaders, Mr Barnier said: “I don’t want to engage or begin any kind of polemics with Arlene Foster.”