First Minister of Northern Ireland Arlene Foster used her speech to the DUP conference to praise Brexit as "Britain's biggest economic opportunity for decades."
She also accused the Irish Government of "talking down" Northern Ireland's economy and "poaching investors".
She made clear her opposition to the return of a hard border when the UK leaves the EU.
"While they seek to take the views of people in Northern Ireland on the issue of Brexit at home, their (the Irish government's) representatives are sent out around the world to talk down our economy and attempt to poach our investors," she said.
"It is clear that the one place that a hard border does exist is in the mind of the Irish government.
"Well, I don't believe in a hard border and am happy to welcome shoppers looking for a bargain across the border anytime they want to come."
The DUP campaigned for a Leave vote in the EU referendum campaign although a majority of people in Northern Ireland voted to Remain.
Speaking about the Brexit referendum, she told the conference audience at the La Mon House Hotel, Belfast: "I respect those who believed that the United Kingdom's best interests were served by remaining within the European Union, but I have no time for those who want to re-fight the referendum.
"That debate is over. Rather than talking up the challenges, we should be looking forward to the opportunities.
"Brexit represents the biggest economic opportunity for this country in decades.
"But, the only way we can ensure that Northern Ireland's interests are best served is if we are united and determined."
Foster was elected leader of the DUP last December (2015) after Peter Robinson stood down. She was the only candidate for election.