Brexit Minister Lord Frost and European Commission vice-president Maros Sefcovic ended their discussions in London on Wednesday with no sign of a breakthrough.
Ahead of the talks Lord Frost warned that time was running out to reach agreement and called on the EU to adopt a "common sense" approach to checks on goods moving from Great Britain to Northern Ireland.
Mr Sefcovic warned that Brussels would act "firmly and resolutely" if the UK unilaterally decided to delay checks intended to ensure there was no return to a hard border with the Republic.
The EU is making multiple complaints against the UK for allegedly failing to uphold the Northern Ireland protocol signed by Boris Johnson in 2019 as part of the Brexit Withdrawal Agreement.
It claims the continued flow of products like chilled meats to flow from the mainland to supermarkets in the Province is putting the sanctity of its single market at risk. It also is demanding faster work on border infrastructure.
However, the British side is bullish, saying the EU is going over the top by banning British products sold in supermarkets and is itself breaking the spirit of the Protocol and also the Good Friday peace accord.
Mr Sefcovic said the EU would act “swiftly, firmly and resolutely” if the UK reneged on the Protocol. He has raised the prospect of a trade war - with Brussels imposing tariffs and quotas on British exports - if the UK falls short on its obligations under the legally-binding agreement.
Following three-and-a-half hours of talks, Lord Frost said they had had a "frank and honest discussion" but that there had been "no breakthroughs" over the Northern Ireland Protocol in the agreement.
He said that the two sides had, however, agreed to carry on talking in an effort to achieve a breakthrough.
"The problem we've got is the protocol is being implemented in a way which is causing disruption in Northern Ireland and we had some pretty frank and honest discussions about that situation today," he said.
"There weren't any breakthroughs. There aren't any breakdowns either and we're going to carry on talking.
"What we really now need to do is very urgently find some solutions which support the Belfast Good Friday Agreement, support the peace process in Northern Ireland and allow things to return to normal."
It came as Joe Biden’s national secutity adviser said the US president had “deep” concerns that a UK-EU trade row could endanger peace in Northern Ireland.
The US president will tell fellow leaders at this week’s G7 summit that gains since the Good Friday Agreement must be protected, Jake Sullivan told the BBC.
If no compromise is reached on the checks on goods, there are fears of potential violence .
Following the talks the European Union warned Britain that it would react swiftly if it acted alone to change post-Brexit trading arrangements for Northern Ireland, but did not spell out what its steps might be.
"Trust, which should be at the heart of every partnership, needs to be restored," Mr Sefcovic told a news conference after the meeting with Frost.
"If the UK were to take further unilateral action in the coming weeks, the EU will not be shy in reacting swiftly, firmly and resolutely to ensure that the UK abides by its international law obligations.
"Pacta sunt servanda," he added, using the Latin for “agreements must be kept”.
The European Union was accused by a Cabinet minister on Wedneday of putting cancer treatment at risk for patients in Northern Ireland by its “rigid” attitude to the Brexit border agreement.
“I hope that we can sort this out because there are things even more important than sausages at stake here,” he told Sky News. “For example, medicines: it really would be absurd if a cancer drug struggled to be dispatched from the mainland of the United Kingdom to Northern Ireland.
“We need to sort this out now.”
His intervention raised the temperature ahead of the showdown talks in London.
Mr Jenrick claimed the Protocol was meant to allow the continued flow to goods from the mainland. “I don’t think either side, when we sign up to the protocol, envisaged that the EU would interpret it in such a rigid and un-pragmatic way.
“We’re asking them to show some common sense and enable something as simple as a sausage to travel from GB to Northern Ireland.”
The UK government has hinted it will act unilaterally to delay checks on chilled meats, such as sausages and chicken nuggets, when the current “grace period” expires at the end of June.
Downing Street said there could be no justification for preventing British-made chilled meats being sold in Northern Irish shops, while Environment Secretary George Eustice said the EU position was “bonkers”.
A senior Conservative accused the Prime Minister of secretly planning to wriggle out of the Brexit agreement from the start. Lord Barwell, who was Theresa May’s chief of staff, said everyone knew what the Protocol would mean for Northern Ireland.
“I find it inconceivable that they didn’t understand what they were signing up to,” he told LBC.
He said Mr Johnson had been desperate for an “oven ready” Brexit deal before the 2019 election and alleged: “So I think the calculation was ‘sign up to whatever is on offer, and then see if we can deal with anything we don’t like down the line’.”