UK’s Brexit negotiator Lord Frost was warned by the Senior US embassy diplomats in London, as well as of US national security adviser Jake Sullivan, that pressure in Northern Ireland will be worsened if he will not square off on border controls.

The US’ encouragement for Britain to settle in an agreement with the EU was the result of the meeting between America’s most senior diplomat in London, Yael Lampert, and Frost, an internal UK government said.

But officials from the US asked regarding a unique rebuke between the partners, or the issuance of a formal demarche by the US to the UK. The US stressed that its function was to push compromise from all involved parties.

 “Any steps that imperil or undermine the Good Friday agreement will not be welcomed by the US,” Sullivan said during a conference on Air Force One before US Joe Biden arrived in the UK.

“The president was not issuing threats or ultimatum … [he] has been crystal clear about his rock solid belief in the Good Friday agreement as the foundation for peaceful coexistence in Northern Ireland. The agreement must be protected,” he added, refusing to clear whether this was what he expected Boris Johnson was doing.

According to a US administration official, Biden is not heightening or directing the issue. “As with any ally we have frank diplomatic conversations. Jake Sullivan spoke to these issues in his BBC interview, which addressed the same themes we have been messaging privately.”

The US seems to suggest that the Biden administration is having a deep interest in the negotiations, although the UK can underscore that it is looking for a friendly settlement with the EU and its approach does not threaten the agreement.