US House of Representatives Speaker Nancy Pelosi has cautioned Britain that if the Northern Irish peace deal is destroyed then there will be no post-Brexit trade deal with the United States.
The US has expressed grave concern that a row between London and Brussels over the implementation of the 2020 Brexit treaty could undermine the Good Friday accord, which effectively ended three decades of violence.
"If there is destruction of the Good Friday accords, they (are) very unlikely to have a UK-US bilateral," she told a Chatham House event in London.
Since the United Kingdom exited the bloc's orbit on January 1, Johnson has unilaterally delayed the implementation of some provisions of the deal's Northern Ireland Protocol and his top negotiator has said the protocol is unsustainable.
The 1998 peace deal largely brought an end to the "Troubles" - three decades of conflict between Irish Catholic nationalist militants and pro-British Protestant "loyalist" paramilitaries in which 3600 people were killed.
The British-run region remains deeply split along sectarian lines 23 years after the peace deal brokered by the United States.
Many Catholic nationalists aspire to unification with Ireland while Protestant unionists want to stay part of the United Kingdom.
The Northern Ireland Protocol aims to keep the province, which borders EU member Ireland, in both the United Kingdom's customs territory and the EU's single market.
The EU wants to protect its single market, but an effective border in the Irish Sea created by the protocol cuts off Northern Ireland from the rest of the United Kingdom - to the fury of Protestant unionists.
Some unionists say the protocol contravenes the 1998 peace deal.
Australian Associated Press