"We could not support any arrangement which could give rise to either customs or regulatory barriers within the United Kingdom internal market", Arlene Foster, leader of the Democratic Unionist Party, said after meeting European Union chief negotiator Michel Barnier.
Earlier Mrs Foster tweeted an image from her meeting with Mr Barnier, emphasising that she will not tolerate any form of barrier between Northern Ireland and the rest of the UK.
He reiterated the EU's line welcoming May's proposals for a bold free-trade deal "without tariffs or quotas" and close security ties after Brexit.
The MP dismissed suggestions that a Canada-style free trade deal would lead to a hard border being created between Northern Ireland and Ireland as a "red herring".
But pointedly, she added: "I do feel strongly that I need to stand up for what is in the national interest".
But he made clear that the European Union envisages a deal involving new customs and regulatory checks on goods travelling from Britain to Northern Ireland, including health and sanitary inspections for 100% of animals and animal products arriving in ports like Larne and Belfast from the rest of the UK.
Technical talks are continuing at official level in Brussels this week, but no visit by Brexit Secretary Dominic Raab has been announced, and Downing Street would say only that new proposals on the border issue would be released "in due course".
After White House visit, Kanye West stops by Apple store in Georgetown
Trump and West previously appeared together shortly after Trump's 2016 election in the lobby of Trump Tower in NY . During one pause, Trump seemed to acknowledge the oddness of the moment, saying, "That was quite something".
Tagovailoa stars as No. 1 Alabama routs Arkansas
Nick Saban's recent comments about Alabama fans appear to have roused something in Tim Tebow. The sophomore was a spectator for most of the second half.
Storm Callum: Donegal's coastal areas 'vulnerable'
The warning for those counties is in place from Friday 12 October 2018 00:01 to Friday 12 October 2018 09:00. Winds of up to 130km are expected, possibly going even higher in coastal areas.
"The data suggest that, in the pursuit of Brexit, Leave supporters across the United Kingdom would be relaxed about a fundamental transformation of the [British] Union but this attitude is not confined exclusively to Leave voters", commented Professor Ailsa Henderson, who led the project alongside Professor Richard Wyn Jones.
Theresa May has urged MPs across the Commons to act in the national interest and back a Brexit deal amid warnings that "decisive" progress is needed in the negotiations before a crunch Brussels summit next week.
There have been suggestions that the political declaration could be as short as six pages in order to push a Brexit deal through and leave disagreements over the future of trade for to be settled during the two-year transition period.
But he also set out key objections to her proposed new trading relationship which involves a UK-EU customs partnership and a "common rulebook" for goods travelling across the border.
With goodwill from both sides, he said an "agreement is within reach" as British Prime Minister Theresa May and her 27 counterparts in the bloc get ready to meet in Brussels on October 17.
"I hope the Prime Minister will not go down the route, which has been suggested".
Mrs May told her Cabinet that Britain will not accept an European Union withdrawal deal without a "precise" political declaration setting out how its requirements on trade and security will be delivered.
But with both sides confirming that differences remain on issues such as the status of the Irish border, expectations are growing that the final moment of decision will be put back to a special summit in November.