US President Joe Biden will later tell PM Boris Johnson not to let the row over post-Brexit trading in Northern Ireland affect the peace process.
The two leaders will have their first face-to-face talks in Cornwall on the eve of the G7 summit.
Mr Biden will stress the need to “stand behind” the Northern Ireland protocol.
They will also discuss transatlantic travel and a new “Atlantic Charter” aimed at refreshing the relationship between the UK and US.
The US President is on his first overseas visit since being elected and the G7 summit is the first time world leaders have all gathered in person since the pandemic began.
The rollout of the coronavirus vaccination programme and climate change are high on their agenda.
But the ongoing dispute between the UK and the EU over regulatory checks on goods going into Northern Ireland from Great Britain is also likely to feature heavily in diplomatic discussions in the coming days.
President Biden has a close interest in Ireland, given his ancestral roots, and had warned that the Good Friday Agreement must not be jeopardised by rows over trade.
Business and political leaders in Northern Ireland have warned that the trade dispute is causing political angst and instability in the run up to the marching season next month, a historical flashpoint between loyalist and nationalist communities.
Protocol ‘only solution’
Northern Ireland was given special status as a result of the 2019 Brexit “divorce” settlement between the UK and the EU.
While England, Scotland and Wales no longer follow EU rules, Northern Ireland still does, because it shares a land border with the Republic of Ireland, an EU member.
In order to avoid a physical border between the two countries – and thereby protect the peace process – it was agreed that customs checks would take place on goods entering Northern Ireland from elsewhere in the UK.
But Unionists say this has effectively put a border down the Irish Sea instead – something they are ideologically opposed to – and business say supply chains have been complicated and disrupted.
Talks on Wednesday between Brexit minister Lord Frost and the European Commission’s Maros Sefcovic to try to resolve the standoff ended without a breakthrough.
Mr Sefcovic said the EU’s patience was “wearing very thin” with the UK’s attitude towards the protocol, after UK ministers said they were prepared to ignore parts of it to prevent disruption to goods like sausages and other chilled meats going to Northern Ireland from Great Britain.
And in a press conference on Thursday morning, European Commission president Ursula von der Leyen said the protocol was the “only solution” to prevent a hard border with the Republic and must be implemented “completely”.
Mr Johnson said on Wednesday that resolving the dispute with Brussels was “easily doable” and “what we want to do is make sure that we can have a solution that…protects the peace process, but also guarantees the economic and territorial integrity of the whole United Kingdom”.
But speaking on a visit to Batley in West Yorkshire, the Labour leader, Sir Keir Starmer, said President Biden had delivered an “an unprecedented rebuke” to the prime minister over the unresolved situation in Northern Ireland.
Sir Keir said he knew “what it means for those communities and the way the government is going about this is undermining the peace process”, adding that the situation was also undermining the UK’s relationship with the US.
“The government needs to make much more of an effort to settle this, to negotiate and get to a settlement for the people of Northern Ireland and for the world.”
It is understood Mr Johnson and President Biden will agree on Thursday to launch a taskforce to make recommendations on safely resuming international travel.
Demand has collapsed as coronavirus restrictions mean people arriving in the UK from the US must self-isolate for 10 days, while most UK citizens are banned from entering the US.
Before the pandemic, the UK-US route was one of the busiest in the world with more than five million people from the UK visiting the US every year, and 4.5 million trips made in the opposite direction.
The new taskforce will be overseen by Transport Secretary Grant Shapps and his US counterparts but aviation leaders have dismissed the plans as lacking clarity.
Virgin Atlantic chief executive Shai Weiss described its creation as “a first step towards reopening the skies” but warned that the “absence of a definitive timeframe” means airlines, businesses and consumers are still in the dark.
The prime minister is coming under fire for his own travel arrangements to Cornwall.
Critics say taking a private jet rather than a train to the summit tarnishes his green credentials and Britain’s claim to be a world leader on climate change.
Mr Johnson defended his decision saying: “If you attack my arrival by plane, I respectfully point out the UK is actually in the lead in developing sustainable aviation fuel, and one of the points in the 10 point plan of our green industrial revolution, is to get to ‘jet zero’ as well.”