Much has been made of the so-called Special Relationship, not least since US President Joe Biden clinched the Oval Office in 2020.
Mr Biden has made no secret of his Irish roots and has appeared, at times, to hold historic suspicions of the UK.
Just this month, he compared Israel's difficult relationship with Palestine to Britain's treatment of Irish Catholics.
But Ms Hartley, who assumed office as ambassador to the UK on July 19, is adamant that Washington still sees London as its key partner.
US President Joe Biden with Prime Minister Boris Johnson Stefan Rousseau
US ambassador to the UK Jane Hartley Wiki Commons
The 72-year-old said: “The relationship between the UK and the US is deep and it’s strong.
“And it’s not just president to prime minister, it’s throughout all of our government.
“There’s no other partner, no other ally, that we work with as closely, whether it be intelligence, security, military, and obviously the importance of economics on both sides of the Atlantic.”
She has also called for further negotiations to find a way to make the Northern Ireland Protocol work.
Ms Hartley said indecision is “never a positive” when it comes to economic investment, as she spoke of the importance of finding a resolution to the current deadlock.
She told Times Radio: “What we’re saying is please have conversations and get this dialogue going again.
“There has to be a way that both sides can come to some agreement, you know, and negotiation and negotiation, everybody always has to give a little.
“But this is an important time. The Good Friday Agreement, it will be 25 years in April. We want what we see up there – the peace, prosperity and security – to continue.
“What we would urge is, please, this is not, we’re not part of this negotiation, but we would urge please sit down, sit down privately, and let’s see if there’s a way to make this work for both sides.”
Her comments come amid a breakdown in relations between Britain and the EU over the Government’s plan to pass legislation at Westminster which would empower ministers to unilaterally rip up the bulk of the Protocol.