US Democratic presidential candidate Joe Biden has intervened in the Brexit standoff between the UK and the EU, warning that a trade deal with Britain relies on its continued respect for the Northern Ireland peace deal “We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit,” Mr Biden wrote on Twitter on Wednesday. “Any trade deal between the US and UK must be contingent upon respect for the Agreement and preventing the return of a hard border. Period,” he added. The tweet was posted shortly after a live press conference with Mike Pompeo, the US Secretary of State, and Dominic Raab, the British foreign secretary. Mr Raab had tried to point the finger at the EU for exploiting the situation in Ireland in the ongoing negotiations for a new trade deal. The intervention by the former vice president shows how UK Prime Minister <a href="https://www.thenational.ae/world/british-government-wins-vote-on-controversial-brexit-bill-1.1077560">Boris Johnson's proposal to override the Brexit divorce treaty</a> signed with the EU is having international repercussions. Critically for the British government, the controversial legislation now threatens a transatlantic free-trade agreement, touted as an important post-Brexit prize. The thorny issue of Brexit has returned to the fore because of disputes over the British government’s contentious Internal Market Bill which passed its first vote in the parliament earlier this week. The law, which still faces further scrutiny in the House of Commons and the House of Lords, would breach international law by giving the government the power to override the Brexit withdrawal agreement. Mr Johnson <a href="https://www.thenational.ae/world/brexit/brexit-eu-prepares-to-grant-britain-three-month-extension-1.929504">hammered out a withdrawal deal with EU leaders that allowed Britain to exit the bloc at the end of January and enjoy a transition in which the terms of trade remain static until the end of 2020.</a> Four senior US congressmen have warned in an open letter that the UK’s plans could have disastrous consequences for the Good Friday Agreement, the 1998 accords which ended the conflict in Northern Ireland. Mr Biden shared the shared the text of the letter in his tweet. “The United States Congress will not support any free-trade agreement between the United States and the United Kingdom if the United Kingdom fails to preserve the gains of the Good Friday Agreement and broader peace process,” it said. “If these reported plans were to go forward, it would be difficult to see how these conditions could be met.” Mr Raab also met Nancy Pelosi, the speaker of the US House of Representatives after his talks with Mr Pompeo in the State Department. She has previously said any British moves to undermine the Irish peace deal would mean there was "no chance" of ratification of a US free trade agreement. A statement following the talks with Mr Raab reiterated the congressional leadership's bottom line for its support. “[We] welcomed his assurances but reiterated the same message that we delivered to the leaders of the UK in London last year: if the UK violates its international agreements and Brexit undermines the Good Friday accord, there will be absolutely no chance of a US-UK trade agreement passing the Congress,” it said. Mr Pompeo said he backed the UK as a trustworthy partner, despite the row over Mr Johnson’s plan to rip up parts of the Brexit deal. “I am confident they’ll get it right,” he said. “We know the complexity of the situation.” The British government has not put a firm timetable on securing a free-trade agreement with the US. The US is the largest destination for British exports outside the EU, and trade between the two countries amounted to $270 billion (Dh991.7bn) in 2019. <a href="https://www.thenational.ae/world/brexit/post-brexit-trade-deal-with-us-is-a-priority-uk-envoy-says-1.971785">A free-trade agreement with the US</a> would boost Britain's GDP by 0.16 per cent in the long run, said a UK government estimate published in March. The co-chair of a committee of American politicians working to protect the Good Friday Agreement, Bruce Morrison, has continued to hit out at the UK its plans. "That deal recognised the importance of the open border on the island of Ireland, and now some of that agreement is being taken back or sought to be taken back by unilateral action by the UK" he told BBC Radio Ulster. "Anything that says 'well we made a deal once, but it's inconvenient now and we're going to recede from that agreement when Northern Ireland is at stake' - we think that's a threat," he added.