Donalds trump special envoy to northern ireland has warned against creating a hard border by accident, as boris johnson presses ahead with new legislation which threatens his brexit divorce deal with brussels.

Mr johnson wants to introduce laws which will limit the eus ability to influence customs arrangements and subsidies in northern ireland if the eu and uk cannot agree a trade deal by the end of the brexit transition period on december 31.

The move, which the uk admits is a breach of international law, has led to a backlash from the eu and senior us politicians in washington who fear a violation of the northern ireland protocol in a no-deal scenario could undermine more than two decades of peace in the region.

Everyone assures me that no one is interested in seeing a hard border between the republic and northern ireland, said mick mulvaney, a former acting white house chief of staff. we appreciate that, we respect that and we agree with that. the one thing i keep trying to assure is on the front of everybodys mind is avoiding a border by accident.

Referring to the peace accord signed by london, dublin and northern ireland political leaders in 1998, mr mulvaney added: the trump administration, state department and the us congress would all be aligned in the desire to see the good friday agreement preserved to see the lack of a border maintained.

Mr trump, who is pro-brexit and a supporter of mr johnson, appointed mr mulvaney as us special envoy to northern ireland in march. the role reflects washingtons support for the peace deal it helped forge more than 20 years ago.

A number of senior democrats, including presidential candidate joe biden and speaker of the house of representatives nancy pelosi, have expressed concerns over mr johnsons move. but mr mulvaneys remarks, in an interview with the ft, are significant because they come from a senior republican with close ties to the trump administration.

On wednesday mr biden said a uk-us trade deal would be scuppered if the northern ireland peace process was undermined by the uks introduction of the internal market bill, echoing similar earlier comments from ms pelosi.

Amid growing concerns over the fallout for the us-uk trade talks, dominic raab, the uk foreign secretary, flew to washington this week for meetings with mike pompeo, the us secretary of state, and ms pelosi.

Our commitment to the good friday agreement and to avoid any extra infrastructure at the border between the north and the south is absolute, he said during his visit.

Mr mulvaney said he had discussed the internal market bill with the irish government, which has joined the eu in calling for britain to abandon the measures that conflict with the northern ireland protocol. the european commission has said it will launch legal action if the uk doesnt rewrite the bill.

He has also spoken with brandon lewis, uk northern ireland secretary, who acknowledged the breach of international law in the house of commons last week.

Mr mulvaney replied not directly when asked whether the uk bill threatens peace in northern ireland. i feel theres so much left to be decided on brexit including the [internal markets bill]. i see nothing in particular that would inevitably lead to a hard border, but again i am simply concerned that everyone be aware of the potential risks.

Tom tugendhat, chair of the uk parliaments foreign affairs select committee, said that the comments by senior republicans and democrats on the legislative measures should concern downing street.

Only two issues in the united states are truly bipartisan: a caution about china and devotion to ireland. its clear the government has a way to go to assuage concerns in washington, he said.

But mr mulvaney said the trump administration would not take sides between the uk and eu. were going to wait and see because the underlying eu-uk trade discussion could end up mooting the [internal markets bill], he said.

Mr bidens intervention was criticised by several senior conservatives on thursday. former cabinet minister iain duncan smith told the times: we dont need lectures on the northern ireland peace deal from mr biden.