THE US Speaker of the House Nancy Pelosi has warned Boris Johnson will have "absolutely no chance" of a trade agreement passing through Congress if he undermines the Good Friday Agreement which ensures an open border on the island of Ireland.

Speaker Pelosi issued a statement last night praising the historic deal, signed in 1998, as the bedrock of peace and an inspiration for the whole world.

"Whatever form it takes, Brexit cannot be allowed to imperil the Good Friday Agreement, including the stability brought by the invisible and frictionless border between the Irish Republic and Northern Ireland.

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"The UK must respect the Northern Ireland Protocol as signed with the EU to ensure the free flow of goods across the border," Pelosi said.

"If the UK violates that international treaty and Brexit undermines the Good Friday accord, there will be absolutely no chance of a US-UK trade agreement passing the Congress," she added.

Earlier, Democratic Congressman Richard Neal told RTE News he had raised concerns over the latest Brexit developments, and their implications for Northern Ireland, with Pelosi.

Congressman Neal is the chairman of the House Ways and Means Committee which will oversee any future US-UK trade agreement.

"I spoke to Speaker Pelosi earlier this morning about what I saw as a threat that could jeopardise the success of the Good Friday Agreement," he said.

"She indicated that she is consistent with my view that any threat that would reimpose a border on the island of Ireland would negate any possibility of having a free trade bilateral agreement with the United Kingdom," he added.

Congressman Neal also spoke to the UK's Northern Ireland Secretary Brandon Lewis.

"The Secretary assured me that he saw no threat of re-establishing a border and he was steadfast in his belief that the Good Friday Agreement remained sacrosanct," Congressman Neal said.

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A group of prominent Irish-Americans known as the Ad Hoc Committee to Protect the Good Friday Agreement, has also expressed concerns about the latest Brexit developments.

"Political leaders and trade negotiators may sabre rattle all they want as they seek to negotiate a much needed trade deal but the Good Friday Agreement cannot be viewed as a bargaining chip," according to a statement from the group.

Meanwhile, a foreign policy adviser to Joe Biden has said that the Democratic presidential candidate is committed to preserving the hard-earned peace and stability in Northern Ireland.

In a tweet responding to the latest Brexit developments, Biden's adviser Antony Blinken wrote: "As the UK and EU work out their relationship, any arrangements must protect the Good Friday Agreement and prevent the return of a hard border."

"I sincerely hope the British government upholds the rule of law and delivers on the commitments it made during Brexit negotiations, particularly in regard to the Irish border protocols," he added.

Like Scotland, Northern Ireland voted to stay in thee EU in 2016, and on Monday its pro-Remain parties warned over-riding the withdrawal deal would amount to a serious betrayal of an international treaty.

Sinn Fein, the SDLP, Alliance Party and Green Party NI voiced concern at the prospect of the Johnson government introducing domestic legislation to supersede parts of the deal's Northern Ireland protocol governing state aid and customs arrangements.

In response to a Financial Times report outlining Johnson's intention, the parties wrote a joint letter to the Government and the EU demanding that the terms of the treaty are honoured.

Under the protocol negotiated in the withdrawal deal, Northern Ireland will continue to follow single market rules for goods and administer the EU's customs code at its ports.

It was designed to avoid a hard border on the island of Ireland, but unionists have been vehemently opposed to it, insisting it instead creates an economic border between Northern Ireland and the rest of the UK.

The letter was signed by Sinn Fein vice president Michelle O'Neill, SDLP leader Colum Eastwood, Alliance leader Naomi Long and Green Party NI leader Clare Bailey.

"It is entirely unacceptable to the Northern Ireland parties that the UK Government would seek to abandon these safeguards and mitigations, which we believe would amount to a serious betrayal of an existing International Treaty," they wrote.

"The economic and political impact on the island of Ireland, on the United Kingdom and above all on the people whom we represent would be devastating, long-lasting.

"It would represent a shocking act of bad faith that would critically undermine the Good Friday Agreement political framework and peace process and the UK's ability to secure other crucial deals to protect the Northern Ireland economy."

The UK and EU are to hold emergency talks later today as tensions rise over Johnson's move to override key parts of the withdrawal agreement.

The EU have insisted they cannot negotiate a free trade agreement with the UK if the UK breaches the Brexit treaty.

Cabinet Office Minister Michael Gove will meet EU official Maros Sefcovic in London to discuss how the development could affect the island of Ireland.

The EU says it wants "clarifications" on the implementation of the agreement.

Meanwhile, trade talks between the UK's Brexit negotiator Lord Frost and his EU counterpart Michel Barnier continue.

Johnson's controversial Internal Market Bill was published in the Commons yesterday.

The legislation gives UK ministers powers to modify or "disapply" rules relating to the movement of goods that will come into force from 1 January, if the UK and EU are unable to strike a trade deal.

The head of the UK government’s legal department quit over Johnson’s proposal ahead of the bill's publication.

Jonathan Jones, the Treasury solicitor and Permanent Secretary at the Government Legal Department, is the sixth senior Whitehall official to resign this year, amid growing tensions between the Prime Minister and staff at the top of the civil service.