Brussels (AFP): Europe's bitter dispute with Britain over post-Brexit trade rules for Northern Ireland will haunt Prime Minister Boris Johnson's G7 summit this weekend.

European Commission president Ursula von der Leyen confirmed Thursday that she would bring up the row when she and fellow EU chief Charles Michel meet Johnson.

Johnson is already under pressure to resolve the stand-off over Northern Ireland from another major guest at the Cornwall summit, US President Joe Biden.

The Times newspaper on Thursday said Yael Lempert, Washington's most senior diplomat in Britain, accused London of "inflaming" tensions in the province -- and in Europe.

The diplomatic rebuke to Brexit minister David Frost "strongly urged" Britain to secure a "negotiated settlement", even if it meant "unpopular compromises".

Biden's spokesman, Jake Sullivan, later said the US president would tell Prime Minister Boris Johnson when the pair meet of his "rock-solid" belief in the Northern Ireland peace deal.

"The agreement must be protected and any steps that imperil or undermine it will not be welcomed by the United States," he told reporters in Cornwall.

But he insisted Biden -- a proud Irish-American with distant family still in Ireland -- would not make "threats or ultimatums".

In Dublin, Ireland's prime minister Micheal Martin called the intervention of the Biden administration "significant" and also "common sense".

Alignment with countries or blocs of similar values was sensible from a US perspective, he said, urging to London to agree to checks on animals, meat and dairy products.

That would "deal with 80 percent of the issues that are causing difficulties and challenges around the protocol," he told Newstalk radio in an interview.

'Peace and stability' 

As part of Britain's post-Brexit withdrawal agreement Johnson signed up to impose some border controls between Great Britain and Northern Ireland.

But, amid worries about unrest among Northern Ireland's pro-British loyalist community, London has suspended checks, triggering a row with Brussels.

Talks between the two sides broke up on Wednesday with no agreement and a threat from European Commission vice-president Maros Sefcovic about possible sanctions.

Of immediate concern to Brussels is London's unilateral extension of a grace period from next month on the transport of chilled meat, including sausages, to Northern Ireland.

British newspapers have characterised any EU retaliatory action as a result as a "sausage war".

Von der Leyen and Michel now plan to bring the matter directly to Johnson.

"Now, we have a treaty on that the withdrawal agreement, it has been signed by both sides... It is important that we now implement the protocol," von der Leyen said.

"We have shown flexibility, we will show flexibility, but the protocol and the withdrawal agreement has to be implemented, completely.

"We will discuss that in a trilateral meeting in Cornwall, together, we are determined to do everything to keep peace and stability on the island of Ireland."

They will host Biden in Brussels on Tuesday next week as part of the US leader's first foreign tour as president.