The Prime Minister’s meeting with US president Joe Biden on Sunday has been cancelled.
The leaders will instead attend a “full bilateral meeting” at the UN General Assembly on Wednesday, No 10 said.
The PM will still meet Irish Taoiseach Micheal Martin, Canadian prime minister Justin Trudeau and Polish president Andrzej Duda in Downing Street on Sunday, as planned.
Downing Street would not provide further details on why the meeting with Mr Biden had been cancelled.
This weekend’s talks are being framed by No 10 as chats, rather than formal bilateral sessions, with politics likely to feature.
The meeting with Mr Biden would have taken place against a backdrop of disputes over the Northern Ireland Protocol and difficulties working towards a trade deal with the White House.
The leaders will instead have their first in-person talks when Liz Truss takes her own trip across the Atlantic to New York for the 77th session of the UN General Assembly next week.
A US official in London confirmed that Mr Biden and his wife, Jill, will still attend the Queen’s funeral on Monday.
Ms Truss is also expected to hold a call with the Crown Prince of Saudi Arabia, Mohammed bin Salman, on Saturday evening.
She spoke to the UAE president and ruler of Abu Dhabi, Sheikh Mohammed bin Zayed Al Nahyan, in the morning, when he expressed his condolences following the death of the Queen, Downing Street said.
There have been no other changes to the weekend’s arrangements.
It comes after Ms Truss met Australian PM Anthony Albanese and New Zealand PM Jacinda Ardern at the Government’s Chevening country residence on Saturday.
In advance of her talks with Ms Truss, Ms Ardern said the Queen’s death and new King would be the “focus of conversation”, and they were also likely to discuss Ukraine and the UK’s free trade agreement with New Zealand.
It was thought the meeting between Ms Truss and Mr Albanese may also touch on trade, with the countries last year signing a deal estimated by the Government to be worth £2.3 billion to the UK economy.
When his British counterpart won the Tory leadership contest earlier this month, the Australian PM tweeted: “I look forward to a continued constructive relationship and friendship between our nations and people.”
Mr Albanese also signed the condolence book at Lancaster House with his partner, Jodie Haydon, during his visit to the UK.
He tweeted: “Today Jodie and I signed the condolence book at Lancaster House.
“In this time of great grief, we are thankful to be here paying our respects to the Queen for her services to duty, faith, family and the Commonwealth.”