Emmanuel Macron, French president, has warned Boris Johnson that efforts to reset relations between Paris and London will fail unless the UK prime minister keeps his word over the Brexit deal in Northern Ireland.

At a breakfast meeting on the margins of the G7 summit in Cornwall, Macron made it clear he expected Johnson to honour the Brexit deal sealed with the EU last December.

The EU has threatened to punish Britain — including imposing trade sanctions — if Johnson unilaterally breaks commitments on border checks made in the Northern Ireland protocol, part of his Brexit deal.

Macron is seen by Downing Street as the most hard line EU national leader on the issue. Arguments between French presidents and British prime ministers at global summits are common — and often play well domestically.

But Macron’s warning underscored the seriousness with which the EU regards the mounting crisis in Northern Ireland.

Joe Biden, US president, has signalled his deep concern over the future of the peace process.

At a breakfast meeting conducted in English, an Elysée source said Macron told Johnson he was ready to reset relations with London and that Britain and France had many common interests.

“The president, however, strongly underlined that this re-engagement requires the British to honour the promises made to Europeans and to respect the Brexit agreement,” the Elysée source said.

The protocol requires Britain to check certain goods moving between Great Britain and Northern Ireland to avoid them passing unchecked across the open border to Ireland, an EU member, and into the single market.

The introduction of an effective trade border within the UK’s territory has infuriated pro-UK unionists in Northern Ireland and added to tension in the region.

Ursula von der Leyen said in a tweet that the Good Friday Agreement and peace on the island of Ireland were paramount.

“We negotiated a protocol that preserves this, signed and ratified by the UK and EU,” she said. “We want the best possible relations with the UK. Both sides must implement what we agreed on. There is complete EU unity on this.”

Johnson argues that the EU is being intransigent in the way it applies the protocol and a clash is approaching later this month on the question of checks on chilled meat products across the Irish Sea.

The EU is banning imports of chilled meat — including sausages and minced beef. A “grace period” to allow continued sale of chilled British meat products in NI expires at the end of June.

Johnson has reserved the right to unilaterally ignore the ban in a move which the EU has warned could trigger retaliation under the terms of the EU/UK Brexit trade and co-operation agreement.

Maros Sefcovic, European Commission vice-president, confirmed last week that this could include trade sanctions, spawning fears of a trade war or — in tabloid headlines — a “sausage war”.

Johnson also held talks on Saturday morning with Angela Merkel, German chancellor, and European Council president Charles Michel and European Commission president Ursula von der Leyen.