Boris Johnson will face renewed pressure from European leaders at the G7 summit in Cornwall to resolve post-Brexit tensions in Northern Ireland, after the British prime minister refused to accept a plan to cut border checks in the region by aligning with EU food rules.

US president Joe Biden’s administration has sought to reassure Johnson that agreeing to mirror Brussels rules on food and animal checks would not hinder prospects for a future UK-US trade deal. But Downing Street insists the idea is a non-starter.

Biden and Johnson discussed Northern Ireland trade rules in their first face-to-face meeting on Thursday ahead of the three-day G7 summit that is starting on Friday.

The UK leader told the BBC that Biden had not expressed alarm over his stance on the issue at Thursday’s meeting.

But Johnson’s meetings with European leaders at the summit may not be as diplomatic. He will meet European Council president Charles Michel and European Commission president Ursula von der Leyen in the margins of the summit on Saturday.

Johnson will also hold bilateral meetings with French president Emmanuel Macron and German chancellor Angela Merkel. He met Italian prime minister Mario Draghi on Friday.

Macron, seen in London as leading a harder line on the Northern Ireland question, warned before the G7 that it was “not serious” to reopen the Brexit agreement.

“I think it’s not serious to want to review in July what we finalised after years of debate and work in December,” the French president said during a press conference on Thursday. “This is not an issue between the UK and France, it is an issue between Europeans and the UK.”

Although Biden was said by Jake Sullivan, US national security adviser, to have “deep” concerns about the state of the peace process in Northern Ireland, the issue did not dominate the president’s meeting with Johnson, UK aides said.

Instead, the British prime minister said the UK-US relationship was not just “special” but “indestructible”, describing the arrival of Biden on the world stage — after four years of Donald Trump’s presidency — as “a breath of fresh air”.

The US has been encouraging Johnson and the EU to reach a compromise on how best to implement the Northern Ireland protocol — the part of Johnson’s Brexit deal that covers the border issue in the region.

The protocol leaves an open border on the island of Ireland — the Republic of Ireland is part of the EU — but sets up checks on certain products moving from Great Britain to Northern Ireland in case they end up crossing into the EU single market.

Commission vice-president Maros Sefcovic again pressed Britain this week to agree to a “Swiss” model, in which the UK would align with Brussels food and agriculture checks to sharply cut the need for border inspections at Irish Sea ports.

The US has been nudging Britain to accept that proposal. Yael Lempert, America’s most senior diplomat in Britain, suggested to David Frost, the UK’s Brexit minister, this month that such an agreement would be backed by Washington.

She said Biden would ensure it “wouldn’t negatively affect the chances of reaching a US-UK free trade deal”, according to a British note of the meeting reported by the Times. Downing Street has not denied the existence of the note, but US officials insist the exchange on June 3 was not “heightened” in tone.

Britain has argued that it needs flexibility to set its own rules — particularly in the sensitive area of agriculture — to secure trade deals with countries with different standards, notably the US.

But allies of Johnson said Britain could never accept that it would be bound by Brussels rules. “It’s a matter of principle,” said one. “We are not going down that route.”

British officials insisted that if Britain applied EU agriculture rules, it would complicate a trade deal with the US given the power of the American farm lobby in US Congress.

But Biden has shown little enthusiasm for an early trade deal with the UK in any event. “It was hardly discussed,” said one official briefed on the president’s talks with Johnson. “It’s not a priority for him.”