Northern Ireland cannot be used as a bargaining chip in Brexit negotiations, Arlene Foster has said.
The Democratic Unionist leader warned politicians in Brussels and Dublin that a deal that involved creating barriers between the North and the rest of the UK was unacceptable.
Mrs Foster's remarks came ahead of a meeting with British Prime Minister Theresa May in Downing Street tomorrow.
The DUP leader, whose party's confidence and supply arrangement with the Conservatives is keeping Mrs May in power at Westminster, will discuss Brexit and the ongoing powersharing crisis at Stormont during talks in London.
Gerry Adams will lead a Sinn Féin leadership delegation to No 10 for a separate meeting with Mrs May tomorrow morning.
Mrs Foster's comments on Brexit come amid calls from senior EU figures and the Dublin government for bespoke customs arrangements for Northern Ireland when the UK leaves the EU, to enable the free-flow of goods across the Irish border.
"Northern Ireland will exit the EU on the same terms as the rest of the United Kingdom," said the DUP leader.
"We will not countenance a border in the Irish Sea. I welcome the Prime Minister's commitment on this point.
"The GB market is not only critical for Northern Ireland but for the Republic of Ireland. We want to see a sensible arrangement that can work for all concerned. The democratic wishes of the British people must be implemented.
"Those in Dublin and Brussels, recklessly trying to use Northern Ireland for their own objectives, should cease. The Prime Minister should warn Brussels that Northern Ireland must not be used as blackmail."
Mrs Foster also rubbished any suggestion that Brexit could result in a return to violence in Northern Ireland.
On the powersharing impasse, she suggested Northern Ireland was edging toward a return to direct Westminster rule unless a deal with Sinn Féin could be reached.
"I want to see local ministers making decisions about Northern Ireland but we cannot continue without a ministerial-led government," she said.
Mrs Foster praised Northern Ireland Secretary Jame Brokenshire for intervening to impose a budget for the North's rudderless public services earlier this month.
"Further steps now look inevitable unless there is a change of direction," she said.