Prime Minister Boris Johnson reiterated his commitment to the Northern Ireland Protocol while appearing on American television on Sunday.
Despite urging from unionists to scrap the protocol, when asked on CBS's Face the Nation programme if he would stick to the Brexit deal agreed with the EU in December the PM replied: "You bet."
Tensions are rising amid unionist claims the protocol cuts Northern Ireland off from the rest of the UK and is causing trade difficulties. Mr Johnson has been urged to invoke Article 16 to suspend the agreement.
The protocol prevents a hard border on the island of Ireland by keeping Northern Ireland aligned with EU rules.
The introduction of the Irish Sea border has led to the appearance of anti-protocol graffiti and posters across Northern Ireland, with MPs and MLAs offices also coming under attack.
New US President Joe Biden, who has strong Irish heritage, has previously stated that Brexit could not be allowed to threaten peace in Northern Ireland and that the Irish border must remain open.
During the appearance Mr Johnson was asked if he could reassure President Biden and the US Congress he would commit to sticking with the Brexit deal "in all circumstances".
"You bet. This is fundamental for us, the Anglo-Irish Agreement, the Peace Agreement, the Good Friday process, the Belfast Agreement, these agreements are absolutely crucial for our continued stability, and success as a UK," the PM replied.
"I have a great relationship with Dublin, with Michael Martin, the Irish Taoiseach. And we're going to work together to do some great things and be in no doubt we don't want to do anything to jeopardize the achievements of the Northern Irish peace process. It's absolutely vital."
Asked specifically about the Northern Ireland Protocol and keeping the Irish border open Mr Johnson said: "We want to make sure that there's free movement, north south, free movement east west, and we guarantee the rights of the people of Northern Ireland, of course."
During the interview Mr Johnson was also asked about his relationship with the new president.
“I’m very delighted, to have a good relationship with the White House, which is an important part of any UK prime minister’s mission,” he said.
“I’ve had some good conversations already with President Biden – fantastic conversations about the way he sees things.
“There’s been some important developments in the way the UK- US thinking has been coming together in the last few weeks, and particularly on issues like climate change, on Nato, on Iran, but above all, on the ways that the US and the UK are going to work together to deal with the environmental challenge that faces our planet."
Mr Johnson said that he also wanted to work with countries like the United States to ensure coronavirus vaccines were made available around the world.
The PM sought to play down Mr Biden’s past description of him as a “physical and emotional clone of Donald Trump” and the former president’s acquittal by the Senate on impeachment charges.
“I think the clear message that we get from the proceedings in America is that after all the toings and froings and all the kerfuffle, American democracy is strong and the American Constitution is strong and robust,” he said.