A row between the United Kingdom and the European Union about the divorce deal they signed as the nation left the bloc could escalate in the coming days, after both sides indicated they are ready to take things to the next level.

Aspects of the deal, known as the Brexit withdrawal agreement, have rankled with the UK government ever since it tried to put them into practice on Jan 1, 2021, and London has repeatedly called on the bloc to renegotiate it.

But Brussels has insisted the legally-binding agreement can and should be made to work, and said London must honor its commitments under the deal.

The Reuters news agency said on Tuesday that the EU will announce measures in the coming days to try to force the UK to abide by the agreement.

Clement Beaune, France's European affairs minister, noted in an interview with Europe 1 radio on Tuesday that the UK depends on energy supplies from the EU.

"Enough already," he said. "We have an agreement negotiated … by Michel Barnier, and it should be applied 100 percent. It isn't being."

He said he had talked to "European counterparts" who were ready to "take measures at the European level or nationally, to apply pressure on the United Kingdom".

France has been particularly perplexed by the UK's refusal of fishing permits for French vessels, despite the withdrawal agreement calling for them to be granted.

"We defend our interests," Beaune said. "We do it nicely, and diplomatically, but when that doesn't work, we take measures."

The Financial Times said a similarly exasperated UK has issued threats of its own, with London saying it will suspend parts of the withdrawal agreement that pertain to trade between the British mainland and the UK province of Northern Ireland. David Frost, who negotiated the withdrawal agreement with Barnier, is seeking a massive rewrite of that part of the deal, which is known as the Northern Ireland Protocol.

Frost said at the annual conference of the UK's ruling Conservative Party that Brussels has not understood how much London dislikes the protocol.

"I urge the EU to be ambitious," Frost said. "It's no use tinkering around the edges. We need significant change."

The protocol, which was put in place to avoid a hard border on the island or Ireland, irks London because it treats one part of the UK differently to the rest, and because it gives oversight to the European Court of Justice.

"We await a formal response from the EU to our proposals," the FT quoted Frost as saying. "But, from what I hear, I worry that we will not get one which enables the significant change we need."

The BBC said Frost claimed suspending the Northern Ireland protocol may be "the only way" forward.

The UK opposition Labour Party's Northern Ireland spokesperson, Louise Haigh, told the BBC: "(David) Frost negotiated every single word of the deal he now discredits at every opportunity, and, as this speech proves, their approach is inflaming tensions while solving nothing."