Leo Varadkar, the prime minister of the Republic of Ireland, has voiced his opposition to Britain’s exit from the European Union, commonly known as Brexit.
We want to build "bridges not borders", Varadkar said in Belfast, Northern Ireland at Queen's University on Friday.
Varadkar reiterated a preference for Britain to remain part of the EU, and failing that, for it to stay in the European single market to maintain the current free trade arrangements between the Republic of Ireland and the United Kingdom.
"Brexit seriously risks driving a wedge between Northern Ireland and Ireland, between Britain and Ireland," Varadkar warned in his first visit to the British-ruled territory on the island of Ireland since taking office in June.
"And I cannot imagine who benefits from that," he added.
"That's our vision for the future: building bridges, not borders," he said.
He said the alternative could mean a return of "hard" customs posts, "a brutal physical manifestation of historic divisions and political failure... a place of bloodshed and violence, of checkpoints. A barrier to trade, prosperity and peace."
Analysts say the return of a "hard" border could disrupt the fragile peace in Northern Ireland, which was plagued by three decades of unrest until a 1998 peace deal.
Ireland, which after Brexit will have the EU's only land border with the United Kingdom, is widely seen as the EU country most exposed to the fall-out from Britain's leaving the bloc.
Varadkar described Brexit as "the challenge of our generation", saying, "Every single aspect of life in Northern Ireland could be affected by the outcome."
Varadkar called on Brexit negotiators to find "solutions" to the problems.
Britain began the two-year Brexit process in March.
Varadkar also urged lawmakers in Northern Ireland to restore the suspended regional government as soon as possible.
Northern Ireland's regional government collapsed earlier this year due to bitter divisions between the pro-British Democratic Unionist Party (DUP) and Irish nationalist Sinn Fein party.