The UK foreign secretary said she discussed the UK's "cast-iron commitment" to the Belfast Agreement during a meeting with US politicians on Saturday.
Liz Truss said it was "great" welcoming a bipartisan US congressional delegation led by top Democratic congressman Richard Neal, with topics of conversation ranging from the peace treaty to "the importance of free trade" and Russia's invasion of Ukraine.
The visit by the US delegation to Britain comes amid tensions over post-Brexit arrangements for Northern Ireland.
Mr Neal, the head of the powerful ways and means committee in the US House of Representatives, also spoke with UK international trade secretary Anne-Marie Trevelyan and British Labour leader Keir Starmer on Saturday.
Accounts of the talks with the British cabinet ministers so far have been thin on detail.
The talks followed a warning from US House speaker Nancy Pelosi that the US Congress would not support a free trade agreement with the UK if the UK government persisted with "deeply concerning" plans to "unilaterally discard" the Northern Ireland protocol, a part of the EU-UK Brexit withdrawal agreement that guarantees a special post-Brexit trading status for the North to avoid a hard Border in Ireland. The protocol has become the source of political tensions for some unionists, and between the EU and the UK amid outstanding issues over its implementation.
Ms Trevelyan said she was “delighted” to welcome the bipartisan congressional delegation led by Mr Neal to her department to discuss UK-US trade matters, as well as the situation in Ukraine, but made no explicit mention of post-Brexit tensions.
A spokesman for Mr Starmer said his meeting with the delegation featured talks on the need to protect the Belfast Agreement by ensuring a working Northern Ireland protocol.
The Labour leader and congressional delegation also touched on the need to be ambitious and creative in trade dialogues between the US and UK, and the importance of western unity in the face of Russian aggression in Europe, the spokesman said.
Strongly worded intervention
In a strongly worded intervention on Thursday, Ms Pelosi urged the UK and the EU to continue negotiations on the post-Brexit trade arrangements to uphold peace in Northern Ireland.
The congresswoman said in a statement: “The Good Friday Accords [Belfast Agreement] are the bedrock of peace in Northern Ireland and a beacon of hope for the entire world.
“Ensuring there remains no physical Border between the Irish Republic and Northern Ireland is absolutely necessary for upholding this landmark agreement, which has transformed Northern Ireland.
"It is deeply concerning that the United Kingdom now seeks to unilaterally discard the Northern Ireland protocol, which preserves the important progress and stability forged by the accords."
The latest controversy on the issue has been sparked by Ms Truss’s announcement on Tuesday that the UK intends to legislate to override parts of the Brexit withdrawal treaty it struck with the EU relating to the protocol.
The foreign secretary told the House of Commons the move was needed to reduce “unnecessary bureaucracy” and to protect the Belfast Agreement.
The ongoing row over the treaty has created an impasse in efforts to form a devolved government administration in Belfast, with the DUP refusing to join an executive unless its concerns over the protocol are addressed.
DUP leader Jeffrey Donaldson described Ms Pelosi's contribution as "entirely unhelpful".
Ms Pelosi is not the only senior figure in Washington to express concern about relations between the UK and the EU in recent days.
Derek Chollet, a senior adviser to US secretary of state Antony Blinken, said on Friday a "big fight" between the UK and the EU was the "last thing" the US wanted.
Mr Neal told the Guardian part of his job was to convince the UK not to breach the Brexit treaty.
“They haven’t breached it yet. They’re talking about breaching it, so part of my job is to convince them not to breach it,” he said.
“My purpose is manifold but we really want to reaffirm America’s unwavering commitment to the Good Friday Agreement and to remind everybody that on the eve of the 25th anniversary of the Good Friday Agreement, it has worked splendidly.
“I want to remind everybody in the UK, in Northern Ireland that it should not be treated as a cavalier achievement.” – PA