DUP MP Sammy Wilson has said he regrets his choice of language after he called Irish prime minister Leo Varadkar "a nutcase".
The DUP's Brexit spokesman made the comment after Mr Varadkar's speech to the European Parliament on Wednesday.
Mr Varadkar said that the UK could not "backslide" on border commitments made during Brexit negotiations last year.
Mr Wilson said Mr Varadkar was "naive, arrogant and inexperienced" for siding with European Union negotiators.
Speaking today, Mr Wilson said that Mr Varadkar's approach would make him popular in Brussels, but that it would "destroy Ireland".
"Upon reflection, I should have said Leo Varadkar's EU policies defy logic rather than the language I used," he said.
Mr Wilson labelled Mr Varadkar "a nutcase" while speaking to the European affairs newspaper, Politico Europe.
The East Antrim MP said the UK government now needed to find some way of "cajoling or enticing" the Irish government to take the "natural position" and "cut [the UK] some slack".
"It was always our view at the very start of this process that the biggest ally we would have when it came to negotiating with the European Union was Dublin," said Mr Wilson.
"That always was the impression we got when Enda Kenny [the former Irish prime minister] was in power, but since this nutcase Varadkar has taken over, things have all changed."
The Department of An Taoiseach declined to respond to Mr Wilson's comments.
The DUP has been contacted for a comment.