The US has delayed its removal of trade tariffs on UK steel and aluminium products amid concerns at the government's approach to the dispute with the EU on post-Brexit trade rules affecting Northern Ireland.
The move was met with a defiant response from Whitehall as a spokesperson said it would not "affect the UK's approach" to the talks with Brussels on changes to the Northern Ireland Protocol - designed to prevent a hard border on the island of Ireland.
The UK has threatened to trigger Article 16 - an emergency brake that allows the UK or EU to seek to suspend parts of the Brexit agreement that introduced some checks on the movement of goods to Northern Ireland from mainland Britain - if they lead to persistent trade difficulties.
Talks between the EU and Brexit minister Lord Frost are continuing, however European Commission vice-president Maros Sefcovic has expressed frustration this week over a lack of UK compromise.
News of the US intervention came last night when the Financial Times was handed a communication from a US Commerce Department official which suggested that talks with the UK on easing metals tariffs could not move ahead.
Watch: Has Brexit made the UK more attractive for illegal migration?
The penalties were imposed on the EU by the administration of former president Donald Trump in 2018 and withdrawn by President Biden in October.
The 25% and 10% tariffs on steel and aluminium imports remain in place for Britain due to its exit from the EU.
The official, the newspaper said, cited US concerns about British threats to trigger Article 16 especially from the US Congress.
In September, US House of Representatives speaker Nancy Pelosi cautioned that there could be no post-Brexit trade deal with Washington if the Northern Ireland peace agreement was destroyed.
A spokesperson for the Department for International Trade confirmed the US stance by responding: "We do not see any connection with this particular issue and the Northern Ireland Protocol and it will in no way affect the UK's approach.
"That is because significant changes are needed to the Protocol in order to protect the Belfast (Good Friday) Agreement and Northern Ireland's place in the UK internal market".
The government suggested it remained in discussions with US officials regarding the tariffs.