DUP leader Arlene Foster has accused foreign affairs minister Simon Coveney of "aggressive" behaviour on Northern Ireland after he voiced support for a united Ireland.
Relations between the DUP and the Irish government have deteriorated markedly since Taoiseach Leo Varadkar came into office in the summer.
And Mrs Foster again heavily criticised the Dublin government for its stance on Brexit.
One of the main bones of contention is Dublin's insistence that Northern Ireland should continue to comply with an EU customs framework when the rest of the UK exits the single market and customs union.
Mrs Foster has insisted that Northern Ireland must be treated the same as Britain, a message she made clear in her party conference speech in Belfast on Saturday.
In an interview with RTÉ, Mrs Foster reiterated her "regret" at the Irish government's position.
But she directed specific criticism at Mr Coveney when challenged about whether the administration's stance on Brexit was motivated by a desire for Irish unity.
"Why then did Simon use this moment in time to talk about his aspiration for a united Ireland in his political lifetime?" she asked.
"I think that's quite aggressive."
Mrs Foster accused Fine Gael's new generation of leaders of indulging in megaphone diplomacy.
"What we should be doing is actually working together to find a way forward, but since this administration came into office, since Leo took over, and Simon became the foreign minister, there hasn't been that same engagement that we had with Enda and Charlie," she said.
Meanwhile, Mrs Foster has written to the heads of each of the 27 EU member states, telling them the DUP will not accept any Brexit deal that creates "barriers to trade" between the north and the rest of the UK.
SDLP leader Colum Eastwood rejected the DUP leader’s comments, saying the "majority of people here voted to remain".
