European Commission President Ursula von der Leyen has told the British Prime Minster there will be no renegotiation of the Northern Ireland Protocol.
In a phone call this morning, Boris Johnson told President von der Leyen that the way the protocol was currently operating was unsustainable.
Solutions could not be found through the existing mechanisms of the protocol, he claimed, which was why the UK had set out proposals for significant changes to it.
He urged the European Union to look at those proposals seriously and work with the UK on them.
Ms von der Leyen said that "the EU will continue to be creative and flexible within the protocol framework. But we will not renegotiate".
"We must jointly ensure stability and predictability in Northern Ireland," she added.
The two leaders agreed to remain in touch on the issue.
Ms von der Leyen's message came a day after UK Brexit minister David Frost demanded that significant changes are made to the terms of the deal he negotiated, saying "we cannot go on as we are".
But he held back from immediately suspending parts of the deal, despite claiming the UK would be justified to take the dramatic step.
President von der Leyen said Mr Johnson "called to present" the proposals to solve the post-Brexit trade issues between Northern Ireland and the UK.
PM @BorisJohnson called to present the UK Command paper on the Irish/Northern Irish Protocol.— Ursula von der Leyen (@vonderleyen) July 22, 2021
The EU will continue to be creative and flexible within the Protocol framework. But we will not renegotiate.
We must jointly ensure stability and predictability in Northern Ireland.
Earlier, Britain's Business Secretary Kwasi Kwarteng said the protocol, which effectively keeps Northern Ireland in the EU's single market for goods, was never "something that was going to last forever".
He told Sky News: "A deal is a deal but it wasn't something that was going to last forever."
"Nobody thought the Northern Ireland Protocol was going to define the role of Northern Ireland within the UK forevermore, it was something that was flexible," he said.
"You'll remember two years ago people said we were never going to get a deal from the EU but we did so. When people say they're not going to look at the protocol again, I say 'well, let's just see'."
The protocol was put in place to ensure there would be no hard border on the island of Ireland.
However, Mr Frost said the economic and social damage caused by the arrangements would have justified the use of Article 16, effectively tearing up parts of the deal.
Additional reporting PA