Joe Biden is "wrong" to have concerns about the Northern Ireland peace deal and does not "fully appreciate" the row over post-Brexit trading arrangements, a Cabinet minister has said.
The US president downplayed the prospects of a trade deal with Boris Johnson during talks at the White House and raised concerns about Northern Ireland's situation.
Biden, who is proud of his Irish roots, issued a fresh warning for the UK not to damage the peace process in Northern Ireland over the EU departure.
He did not counter the assertion from his predecessor Barack Obama that Britain would be at the "back of the queue" for a post-Brexit free trade agreement.
Environment Secretary George Eustice suggested Biden's concerns about Northern Ireland were based on "just reading the headlines" and listening to accounts from the European Union.
The Prime Minister and US president held talks at the White House on Tuesday.
Sitting next to Johnson in the Oval Office, Biden told reporters: "We're going to talk a little bit about trade today and we're going to have to work that through."
He said he felt "very strongly" about issues surrounding the peace process, as problems with the Northern Ireland Protocol persisted.
"And I would not at all like to see - nor, I might add, would many of my Republican colleagues like to see - a change in the Irish accords, the end result having a closed border in Ireland," he said.
Johnson said "that's absolutely right," adding: :On that point, Joe, we're completely at one, nobody wants to see anything that interrupts or unbalances the Belfast/Good Friday Agreement."
Downing Street said the Prime Minister updated Biden on developments with the protocol since they last met in June.
"The leaders agreed on the importance of protecting peace in Northern Ireland."
The White House said Biden "reiterated his longstanding support for a secure and prosperous Northern Ireland in which all communities have a voice and enjoy the gains of the hard-won peace."
The UK is seeking to renegotiate the terms of the Brexit deal with the EU.
The protocol means Northern Ireland is effectively in the EU's single market for goods, to avoid a hard border with Ireland, which creates a trade barrier for products crossing the Irish Sea from Great Britain.
Eustice told Sky News: "(Biden) is probably at the moment just reading the headlines, reading what the EU is saying, reading what Ireland might be saying, which is that they would like the Northern Ireland Protocol to work in the way the EU envisage.
"We think he is wrong because the truth is that unless we have a sustainable solution that enables trade to continue between GB and Northern Ireland then we are going to have issues, and that itself would become a challenge to the Belfast Agreement.
"We will obviously explain to the United States effectively it is tantamount to saying that potatoes grown in one part of the United States can't be sold in another part of the United States.
"When you explain some of those provisions in detail, it is understood by the US government that that clearly does not make any sense and therefore should be revisited.''
Eustice said the protocol was "very complicated" and "I'm not sure he (Biden) does fully appreciate all of that."
The Prime Minister's first White House meeting with Biden came as the British government's hopes for securing a comprehensive free trade deal with the US faded.
Ministers are instead considering whether to join an existing pact with the US, Mexico and Canada to boost transatlantic trade, in a major departure from their prior ambitions.
Eustice said "we still very much hope to be able to put together an agreement with the United States" but "it's just not a priority" for the Biden administration.
