Arlene Foster has warned Taoiseach Leo Varadkar against "disrespecting" the decision of the United Kingdom to leave the European Union.
Ahead of her party's meeting with Mr Varadkar tomorrow - during his first official visit to Northern Ireland - the former First Minister described recent remarks by the Fine Gael leader as unhelpful.
Mr Varadkar had insisted he would not help design a post-Brexit border or work out how it should operate, which brought a warning from DUP MP Sir Jeffrey Donaldson against any return to "megaphone diplomacy" from Dublin.
Mrs Foster said she was "looking forward" to the meeting, but dismissed Mr Varadkar's expression of hope that the UK will remain in the EU despite last year's referendum result.
"He may be hopeful, but that is disrespecting the will of the British people. Brexit is going to happen. We are leaving the European Union," she said.
"I just hope the Republic of Ireland will continue to work constructively with us in Northern Ireland and the rest of the UK, because it is very much in their interest to have a Brexit that works for them, as well as a Brexit that works for the UK."
Referring to the Irish Government's decision to back Sinn Fein and SDLP demands for a stand-alone Irish Language Act - a key issue in the stalled talks to restore devolution - Mrs Foster (below) said the Taoiseach and other Irish ministers "should reflect on whether they are being helpful to the process here in Northern Ireland or not". "They have made various interventions recently in relation to Northern Ireland politics. It would be better if we focused on finding solutions to what is in front of us. We want to find ways forward," she said.
"We know there are huge opportunities in relation to Brexit and we also accept there are short-term challenges.
"To overcome all of that we have to work together.
"The sort of megaphone diplomacy that has been engaged in is not helpful.
We have to work together to get a European exit that works for everybody."
Mr Varadkar, who is also meeting most of the other main parties involved in the negotiations, will give a major address at Queen's University focused on north-south relations.
The Ulster Unionist Party said it will not meet Mr Varadkar during his visit, but denied it was a calculated snub.
It said it was not in a position to meet the Taoiseach, who is to take part in a Pride event in Belfast on Saturday, because of "logistics".
"We look forward to meeting Mr Varadkar in the not-too-distant future, where we will be discussing the issues around Brexit, his approach to relationships across these islands and also seeking a response to our request for information held by the Irish Directorate of Military Intelligence on terrorist atrocities such as Kingsmill to be made available to the appropriate authorities here," the party said.
Meanwhile, TUV leader Jim Allister bluntly told Mr Varadkar to keep his nose out.
"I believe it is totally inappropriate for him to attempt to interfere with the internal affairs of Northern Ireland," the North Antrim MLA said.
"The legal definition of marriage is a Northern Ireland issue, not the plaything of foreign governments."
Sinn Fein president Gerry Adams welcomed Mr Varadkar's decision to attend a breakfast Pride event in Belfast on Saturday.
"That's good, and an important act of solidarity with the LGBT community," he said.
"It will help focus attention on the need for marriage equality, available elsewhere throughout these islands, to be extended to citizens in the North."
Mr Varadkar revealed he was gay in the run-up to the Republic's referendum on same-sex marriage in 2015.
He told the Pride parade in Dublin in June he intends to "press for marriage equality across Ireland".
But asked if his attendance at a Pride event in Belfast might cause annoyance to the DUP - which is opposed to same-sex marriage and used the Assembly petition of concern mechanism to block the issue last year - Mr Varadkar said he would make no compromises about his views.
Same-sex marriage has now become one of the key issues in the talks to restore power-sharing at Stormont.
Northern Ireland is the only part of Britain and Ireland where same-sex marriage is unlawful.