Britain's former Brexit minister, David Frost, has accused the Biden administration of not fully understanding Northern Ireland and the impact of the Northern Ireland Protocol.
He also said Britain does not need lectures from others about the Good Friday Agreement.
During a speech at a leading Conservative think-tank in Washington DC, Mr Frost said the protocol needs changing or replacing, and he urged the British government to unilaterally legislate to do away with part or all of the protocol.
Asked about negotiations with the EU on changes to the protocol, he said: "I think we've reached the end of the road on that in the last week or so. I think the government's got no choice but to act unilaterally.
"The protocol is clearly undermining the Belfast Good Friday Agreement - the institutions are not workable. The protocol has destroyed consent amongst unionism for these arrangements and you can't carry on like that."
He also said removing the protocol was an issue of sovereignty for the UK government.
Britain's former Brexit minister, David Frost, has accused the Biden administration of not fully understanding Northern Ireland and the impact of the Northern Ireland Protocol | Read more: https://t.co/1t72MfsfmI pic.twitter.com/gmDsSuWY0T— RTÉ News (@rtenews) May 13, 2022
"It is fundamental the British government must be able to govern the same country, and we're getting to a point where that is becoming difficult again, in Northern Ireland. So it must act, and bringing forward legislation is the right thing to do for the unity of the country, and I hope everyone will support them, and that they have the determination to see this through".
He said he was aware that the Biden administration was paying close attention to the way the UK government is dealing with the protocol issue, but said: "I am not convinced the niceties of Northern Ireland are well understood. I get slightly frustrated when we are told by a third party - albeit a very important one in this context - how to manage these issues. It's our country that had to face terrorism, so we don't need lectures from others about the peace process and the Good Friday Agreement."
Mr Frost said: ""In the end it has got to be our judgement about what is needed to preserve that agreement and preserve the unity of the country and the consent of everybody in Northern Ireland for these arrangements."
"We have just reached the end of the road and we are going to have to act".
The host of the event, Dr Nile Gardiner of the Margaret Thatcher Foundation for Freedom, said it was a matter of British sovereignty and British self determination and the future of the union.
"You have politicians here in the United States, some of them openly backed to the IRA and are now lecturing Britain over the Northern Ireland Protocol and making all manner of interventions on this without appreciating that the protocol is actually a major threat to the Good Friday Agreement".
Dr Gardiner, who is British, criticised President Joe Biden and Speaker of the House of Representatives Nancy Pelosi for linking the protocol to the question of a US-UK trade deal, calling it "a direct intervention in British affairs".
Mr Frost said whilst a UK-US trade deal would be nice, he did not believe one would materialise soon because of the politics of the US, which is not in favour of extending trade deals to any country for the time being.
In his opening speech to the influential think-tank, Mr Frost urged the Biden administration to be "cautious in what they say and do. Honestly, I am not convinced that the niceties of Northern Ireland are well understood by this administration, and I hope they will think hard before telling a friendly government how to protect the unity and territorial integrity of their own country".
Yesterday, Taoiseach Micheál Martin said that a "unilateral legislative initiative" by Britain to circumvent the Northern Ireland Protocol would have a "very destabilising effect on the Good Friday Agreement".
He warned that unilateral action on the protocol would be in breach of an international treaty.
British foreign secretary Liz Truss said that the situation in Northern Ireland was now a matter of the internal security of the United Kingdom.
Her comments yesterday came after a phone call between Ms Truss and her EU counterpart Maroš Šefčovič on the UK's plans to dismantle the Northern Ireland Protocol.
Mr Šefčovič said the EU would do its utmost to protect Ireland's single market membership.