A US-UK trade deal does not will get through Congress if Brexit breaks the Good Friday Agreement, US House of Representatives spokesperson said.
Democrat Nancy Pelosi, whose party controls the House, said the UK's exit from the EU would not allow the Irish peace deal to be jeopardized.
His comments came after the US national security adviser said the UK would be the "first line" for a trade deal.
- UK & # 39; first line & # 39; for the US trade deal, says Bolton
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The redistribution of borders between Northern Ireland and the Republic of Ireland if the UK leaves the EU without a mutual agreement on 31
"Whatever formula it requires, Brexit cannot be allowed to imperil the Good Friday Agreement, along the borderless border between the Ireland Republic and Northern Ireland," Mr Pelosi said in a statement on Wednesday.
& # 39; The stout hunt & # 39;
Mr. Bolton said on Tuesday that the Trump administration had supported a no-Brexit deal, adding that Washington would propose an accelerated series of trade deals in case one.
He stated that these could be done on a "sector-by-sector" basis, with a prior labor agreement. A trade deal for financial and agricultural services is not the first to be agreed upon, he added.
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Asked if his proposed plan was to follow the rules of the World Trade Organization (WTO), Mr. Bolton said "our trading business. It seems to think so".
He stated that there was enthusiastic bipartisan support in Congress for the rapid enactment of each phase.
Mr. Johnson said there were "all kinds" of opportunities for UK business in the US, particularly service companies, but negotiations would be a "tough old worry".
However, critics have warned that the UK will have to grant certain requests to the US in exchange for any trade agreement.
Former UK Secretary of State Jack Straw, who served under a Labor government, described Mr. Bolton as a "dangerous bell".
He suggested that the UK would have to agree to certain requests in the United States, for example allowing US imports of poultry to be consumed by the US.
"This is a highly transactional administration … you don't get something for nothing," he told BBC Radio 4's Today program.
Lewis Lukens, a former US embassy mission representative in London and former acting US ambassador, said Mr. Bolton was in line with President Trump's "America first agenda" and would make "strong requests" "in the UK to back the US position on issues such as China, Iran and Chinese tech giant Huawei.
Mr Johnson is expected to have his first face-to-face meeting with the prime minister with Mr. Trump later this month at the G7 summit in France.