UK Prime Minister Liz Truss (L) and US President Joe Biden. Photo: AFP
The White House has warned again that dismantling the Northern Ireland Protocol would "not create a conducive environment" for US-UK trade talks.
President Joe Biden's press secretary, Karine Jean-Pierre, said such actions could harm the Good Friday Agreement that hit an end to decades of political violence.
The warning comes as the new Northern Ireland secretary said he wanted to "negotiate a solution" with the EU.
However, Chris Heaton-Harris told MPs the government would still legislate if this did not happen.
Speaking to reporters on Wednesday (local time), Jean-Pierre said: "There is a no formal linkage on trade talks between the US and the UK and the Northern Ireland Protocol, as we have said, but efforts to undo the Northern Ireland Protocol would not create a conducive environment."
Biden has previously said that he felt "very strongly" about the protocol and has repeatedly urged the UK not to take any action that could potentially create a hard Irish border.
Biden raised the issue of the protocol directly with Liz Truss yesterday during their first phone call.
A read-out of their conversation from the White House said the pair discussed "the importance of reaching a negotiated agreement with the European Union".
What is the protocol?
The protocol is the part of the Brexit deal that keeps Northern Ireland in the EU's single market for goods, avoiding a hard border with the Republic of Ireland.
The arrangement ensured free trade could continue across the Irish land border, which is a sensitive issue because of the history of conflict in Northern Ireland.
But the protocol brought in some new checks on goods moving between Great Britain and Northern Ireland and has been criticised by unionist politicians.
However, the majority of politicians elected to the Northern Ireland Assembly in May's elections support the arrangements.
The Democratic Unionist Party (DUP) has refused to re-enter a power-sharing government in Northern Ireland until its concerns about the protocol are resolved.
Speaking on her first full day in office, Truss told the Commons that the Northern Ireland Executive must return.
In response to a question from the SDLP's Colum Eastwood, Truss said she wanted to "work with all of the parties in Northern Ireland to get the executive and the assembly back up and running so we can collectively deliver for the people of Northern Ireland".
"But in order to do that we do need to fix the issues of the Northern Ireland Protocol which has damaged the balance between the communities in Northern Ireland," she said.
"I'm determined to get on with doing that and determined to work with all parties to find that resolution."
The executive collapsed in February after the DUP withdrew its First Minister Paul Givan over its objections to the protocol.
Truss was then asked by former NI secretary Shailesh Vara if the government would press ahead with the NI Protocol Bill if it could not reach an agreement with the EU.
"We need to resolve the issue of the Northern Ireland Protocol," she replied.
"My preference is for a negotiated solution, but it does have to deliver all the things that we have set out in the Northern Ireland Protocol Bill.
"And what we cannot allow is for this situation to drift, because my number one priority is protecting the supremacy of the Belfast/Good Friday Agreement."
Heaton-Harris called on the DUP to return to power sharing as soon as possible, but insisted he understood the importance of resolving issues with the protocol first.
He is expected to meet party leaders in Northern Ireland on Thursday.
Heaton-Harris is the third Conservative MP to hold the NI secretary role within the past three months, and replaces Vara who was sacked on Tuesday.
Vara, who was in the role for 62 days, became the shortest serving Northern Ireland secretary ever.
Steve Baker appointed to NI Office
Meanwhile, Steve Baker has replaced Conor Burns as minister of state in the Northern Ireland Office.
His appointment has just been confirmed by Downing Street.
Baker was also a chair of the pro-Brexit European Research Group of Conservative MPs for several years.
In March, he called on the government to trigger Article 16 of the Northern Ireland Protocol, a mechanism to suspend parts of the deal.
The MP for Wycombe, he also co-chaired a group of MPs opposed to Covid restrictions.
- BBC