The Speaker of the US House of Representatives has warned London there will be "absolutely no chance" of a US/UK trade deal if Boris Johnson overrides the Brexit deal with Brussels.
emocrat Nancy Pelosi said the US Congress would never pass an economic agreement that it felt could "imperil" the Northern Ireland peace accord.
In a statement yesterday, Ms Pelosi said: "The Good Friday Agreement is the bedrock of peace in Northern Ireland and an inspiration for the whole world.
"Whatever form it takes, Brexit cannot be allowed to imperil the Good Friday Agreement, including the stability brought by the invisible and frictionless border between the Irish Republic and Northern Ireland.
"The UK must respect the Northern Ireland Protocol as signed with the EU to ensure the free flow of goods across the border.
"If the UK violates that international treaty and Brexit undermines the Good Friday accord, there will be absolutely no chance of a US-UK trade agreement passing the Congress. The Good Friday Agreement is treasured by the American people and will be proudly defended in the United States Congress."
Meanwhile, the European Union is considering legal action against the UK for pressing ahead with plans to override parts of the Withdrawal Agreement.
The bloc believes it may be able to mount a challenge before the British Government can pass legislation that changes part of the deal struck last year relating to Northern Ireland - a move that ministers admit would breach international law in a "very specific and limited way".
According to Bloomberg, a draft working paper prepared by Brussels and circulated to member states warns that the UK Internal Market Bill represents a "clear breach" of the agreement which would "open the way to legal remedies".
It adds that once the transition period ends, the EU could also trigger the dispute settlement mechanism contained in the deal, which could ultimately result in the UK being hit with financial sanctions.
The reports emerged as the EU called for emergency talks and warned Mr Johnson that reneging on the Withdrawal Agreement would bring about no deal.
Maros Sefcovic, European Commission vice-president, yesterday said he would meet his UK counterpart Michael Gove today to outline the bloc's "strong concerns".
He added: "The Withdrawal Agreement is not open for renegotiation and we expect the letter and the spirit of the Withdrawal Agreement will be fully respected."
Commission President Ursula von der Leyen said she was "very concerned" following the tabling in the UK parliament of the Internal Market Bill, which ministers have admitted will breach international law.
As talks continued in London on a post-Brexit, free-trade agreement, she said such actions would "undermine trust" and called on the prime minister to honour his past commitments.
Her warning came as John Major became the latest senior Conservative to denounce Mr Johnson's decision to go back on assurances he had made in an internationally binding treaty. "For generations, Britain's word - solemnly given - has been accepted by friend and foe. Our signature on any treaty or agreement has been sacrosanct," the former prime minister said in a statement.
The legislation would allow Britain to override key elements of the Withdrawal Agreement to insist on no export paperwork for goods moving from Northern Ireland to England, Scotland or Wales, and to restrict the use of EU state-aid rules. Ministers argue the changes are necessary to ensure that the province has "unfettered access" to the UK market in the event of no deal.
Separately, tensions escalated last night as EU officials hit back at claims that a threat of blocking the export of British food and agriculture products to Northern Ireland had been used as "leverage" in the negotiations.
Michel Barnier, the EU's chief negotiator, arrived in London yesterday, with sources indicating he would confront his opposite number, David Frost, over the UK plan to change parts of the deal.