Chip Somodevilla/Getty Images Nancy Pelosi says no UK-US trade deal if Brexit risks Irish peace Senior US Democrat issues warning after John Bolton said Britain would be at the ‘front of the trade queue’ with Washington after Brexit.

LONDON — Nancy Pelosi, the speaker of the U.S. House of Representatives, warned Boris Johnson and Donald Trump that Congress will block any trade deal between the U.K. and U.S. that threatens peace in Northern Ireland.

According to a statement from her office, Pelosi said Brexit “cannot be allowed to imperil” the Good Friday Agreement that ended decades of conflict.

British Prime Minister Johnson has demanded the EU scrap the backstop plan to keep the Northern Irish border open, which was negotiated by his predecessor Theresa May. But Brussels has refused to budge, increasing the possibility of a no-deal Brexit and border checks.

Pelosi, a Democrat, issued her warning after U.S. National Security Adviser John Bolton said during a visit to the U.K. on Tuesday that Britain would be at the “front of the trade queue” with Washington after Brexit.

She said in a statement: “Whatever form it takes, Brexit cannot be allowed to imperil the Good Friday Agreement, including the seamless border between the Irish Republic and Northern Ireland, especially now, as the first generation born into the hope of Good Friday 21 years ago comes into adulthood. We cannot go back.”

She added: “If Brexit undermines the Good Friday accord, there will be no chance of a U.S.-U.K. trade agreement passing the Congress.

“The peace of the Good Friday Agreement is treasured by the American people and will be fiercely defended on a bicameral and bipartisan basis in the United States Congress.”

It comes after senior members of Congress vowed to block any trade deal between the U.K. and U.S. that jeopardizes the 1998 pact.

Bolton also said during his U.K. visit that the Trump administration would "enthusiastically" support a no-deal Brexit.