President Joe Biden and Prime Minister Liz Truss have agreed on the "priority" of preserving peace in Northern Ireland as they discussed its post-Brexit trade arrangements in their first talks.
They held their first one-on-one meeting at a UN summit in New York.
There have been tensions between them over UK plans to override the Northern Ireland Protocol.
Before the meeting, both said they were "committed" to maintaining an agreement that brought peace in Northern Ireland.
Ms Truss's spokesperson said she and Mr Biden only had a "short discussion" about the Northern Ireland in a wide-ranging conversation dominated by the war in Ukraine.
A Downing Street read-out of the meeting said the leaders talked about supporting Ukraine, energy security and preventing Iran from acquiring a nuclear weapon.
The prime minister's spokesperson said the tone of the meeting was "warm" and that they did not discuss a UK-US trade deal.
In opening remarks at the beginning of their meeting, the US president told Ms Truss he was "looking forward to hearing what's on your mind" about Northern Ireland.
He congratulated her on becoming prime minister and said he looked forward to working closely with her, calling the UK "our closest ally in the world".
Ms Truss told the president the UK and the US were "steadfast allies" as she thanked him for his support following the death of the Queen.
"Of course I'm looking forward to discussing the Belfast Good Friday Agreement and how we make sure that's upheld into the future," she added.
Earlier in the day, Ms Truss also discussed the Northern Ireland protocol with European Commission President Ursula von der Leyen.
But Ms Truss declined to discuss the protocol with France's President Emmanuel Macron on Tuesday.
Both Mr Biden and Ms Truss have said a negotiated resolution to the row between London and Brussels over the protocol is preferable.
Mr Biden and Ms Truss were originally scheduled to meet in London on Sunday, after the president travelled to the UK for the Queen's funeral, but that meeting was postponed.
The Northern Ireland Protocol is part of the Brexit deal: it means lorries don't face checkpoints when they go from Northern Ireland (in the UK) to the Irish Republic (in the EU)
Instead, when goods arrive in Northern Ireland from the rest of the UK (England, Scotland and Wales), they are checked against EU rules
The UK and the EU chose this arrangement because the Irish border is a sensitive issue due to Northern Ireland's troubled political history
Read more: Guide to the Brexit border problem
The Northern Ireland Protocol is the post-Brexit agreement which allows for special trading arrangements between the Republic of Ireland and Northern Ireland.
It keeps Northern Ireland in the EU's single market for goods, avoiding the need for a hard border between the UK and Ireland after Brexit. It was signed when Boris Johnson was prime minister.
But it has been a source of tension since it came into force at the start of 2021.
Currently there is no functioning devolved administration in Northern Ireland because the Democratic Unionist Party (DUP) - the second-largest party in the recent Stormont elections - oppose the protocol and refused to take part in a power-sharing government until its concerns are resolved.
Earlier this week, the UK government told the EU it would continue delaying customs checks on goods moving from Great Britain to Northern Ireland, despite ongoing legal action from Brussels over this stance.