The US special envoy to Northern Ireland has warned against creating a 'hard border by accident' on the island.
In an interview with the Financial Times, Mick Mulvaney said: "The Trump administration, State Department and the U.S. Congress would all be aligned in the desire to see the Good Friday Agreement preserved to see the lack of a border maintained."
His comments come as the Government proposes new legislation that would override aspects of the Withdrawal Agreement which was signed by both the EU and UK in October.
If implemented, the Internal Market Bill will end the legal legitimacy of the Northern Ireland protocol - contained within the Withdrawal Agreement - in areas such as customs and state aid and financial assistance.
The Democratic presidential candidate said any trade deal between the UK and the US "must be contingent upon respect for the Agreement and preventing the return of a hard border."
The Foreign Secretary, Dominic Raab, has previously said the UK had “absolute” commitment to the Good Friday Agreement and accused Brussels of the “politicisation” of Northern Ireland issues in the context of Brexit trade talks.
Mr Mulvaney, who is an Irish-American with strong links to Co Mayo where his grandparents are from, has held the post since March.
He had previously served as US President Donald Trump's acting Chief of Staff.
Mr Mulvaney is also expected to visit to Northern Ireland in the coming weeks.