The US Special Envoy to Northern Ireland Mick Mulvaney has said that the entire federal government is agreed that if there is a return to a hard border on the island of Ireland then any potential trade deal with the UK will not go ahead.

Speaking to RTE News on his first official visit as envoy to Dublin, Mr Mulvaney said that the US would do whatever it could to prevent a return to a hard border and to protect the Good Friday Agreement.

He said members of Congress were correct to have written to the British Prime Minister Boris Johnson to tell him that Congress would not support any free trade agreement between the UK and the US that "failed to preserve the gains of the Good Friday Agreement and broader peace process".

"Their attitude is 'look the British need to know that if a border goes up, then all deals are off. I think that's the accurate position of the entire federal government".

He said the United States would "protect and defend" the Good Friday Agreement and does not want to see it damaged.

Speaking in an interview broadcast on RTÉ's Six One news, Mick Mulvaney said that the US was "cautious" and "watching the situation" in light of the UK's Internal Markets Bill.

He said that although the Northern Ireland Secretary of State Brandon Lewis had admitted the Bill would break international law, he viewed the piece of legislation as a preventative measure.

He echoed the views of his boss US Secretary of State Mike Pompeo in saying that he still trusted the UK, in spite of this.

Mick Mulvaney is visiting Dublin, Belfast and London on his trip and said he had come to get a sense for himself of what was going on here and to appeal for "cool heads" in this final push for the EU and the UK to agree a deal.

He met the Taoiseach, Minister for Foreign Affairs, and the Sinn Fein President Mary Lou McDonald in Dublin today and has meetings with the Northern Ireland leadership tomorrow.

He said the concerns surrounding the Internal Markets Bill became "more potentially relevent" with each passing day, and that was why he had travelled to Ireland this week.

He does not have a direct role to play in the negotiations, but said his attitude was to "let everybody calm down" and to "take a deep breath".

He said he was "cautiously optimistic" that negotiations were going in the right direction.

He said he felt the UK would be able to do a trade deal with the EU soon but that while the US was not concerned about a return to a hard border on the island, it was paying attention because a risk existed.

He also said he was looking forward to the US securing a free trade agreement with the UK.

He said from the American perspective one of the "benefits of Brexit" was that the UK could now hold negotiations with the UK, something it could not do with Ireland because of its existing EU membership.

"We don't have any stronger ties than with Ireland and the UK, we're practically family".

Although the US election is just five weeks away, the US Special Envoy, the former Congressman and Chief of Staff to President Trump, said that the timing of his visit was not designed to drum up support for the President among Irish American voters.

"This is the fifth or sixth time this trip has been scheduled," he said.

"As is often the case with local politics, it was not appropriate for me to come on the tail-end of the (Bobby) Storey funeral, or on the tail-end of the golf event. It's one of those things you deal with when dealing with diplomatic matters, you have to go at a time that is diplomatically acceptable".

He also said it would not have been appropriate to come in the early days of the Covid19 pandemic.

He added "they told me not to bring my golf clubs." "That's fine, I get it", he said, lamenting that Sunday, when he arrived had been perfect golfing weather.

Currently visitors arriving to Ireland from the US have to restrict their movements for 14 days. The Irish Government has waived this requirement for Mick Mulvaney on diplomatic grounds.

Speaking in Belfast yesterday after meeting Northern Ireland Secretary Brandon Lewis, Mr Mulvaney said he believes the European Union and the UK are going to be able work out Brexit in a way that is acceptable to everybody. 

The former chief of staff to US President Donald Trump was appointed to the vacant US Special Envoy position in March. 

This is Mr Mulvaney's first visit to Ireland in the new role. He met the Northern Ireland Secretary and the DUP leader in Hillsborough yesterday.

Additional reporting Tommie Gorman