The UK is "at war" with the United States over Ireland and Brexit, Gordon Brown has said.
The former Labour prime minister said Boris Johnson's government would never be able to sign a trade deal with the US until the issues were solved.
It comes as Boris Johnson escalates the row over the territory with controversial new legislation.
Many Democrats in the US Congress see themselves as the guardians of Good Friday Agreement, which ended the Troubles.
They have taken a dim view of what they see as UK brinkmanship over the border with the republic, which is related to Brexit.
"We're at war with America over Ireland because America will not sign a trade treaty with Britain as long as we cannot sort out the issues related to Ireland," Mr Brown, who was prime minister between 2007 and 2010, told the Beth Rigby Interviews programme on Sky News.
The ex prime minister said that even if Joe Biden came around to a trade deal, many in the US congress would not.
"He may think that but the American congress will not think that," he said.
"There's no chance of a trade deal between Britain and America unless we can sort out the problems that are arising in Ireland, and, of course, there's no chance of getting better trade relationships with Europe unless we can sort these problems out as well.
"And that's very much part of our future because if we cannot export to the leading markets in the world, and cannot do so successfully with these new industries and new technologies, then the cost-of-living crisis will be with us for years and not just temporarily."
The UK and EU agreed a solution to the Northern Ireland border issue during Brexit talks which would keep the frontier with the Republic open, in accordance with the Good Friday arrangements.
But as part of the solution the UK agreed to impose new checks on trade between Northern Ireland and Great Britain.
Though the protocol has general support in the territory, it has angered some in the unionist community, and Boris Johnson and his ministers now say the arrangements they negotiated are not working.
He has brought forward new legislation to give himself powers to override the agreements, which the EU's chief negotiator Maros Sefcovic last night described as a "gun on the table".
In September 2020 Joe Biden summarised US fears over UK policy by stating: "We can’t allow the Good Friday Agreement that brought peace to Northern Ireland to become a casualty of Brexit.
"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."
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