The Prime Minister’s meeting with US president Joe Biden on Sunday has been cancelled.
They 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.
No 10 would not give any further details on why the meeting with Mr Biden was cancelled.
Ms Truss is also expected to hold a call with the Crown Prince of Saudi Arabia, Mohammed bin Salman, on Saturday.
She spoke to the UAE president and ruler of Abu Dhabi, Sheikh Mohammed bin Zayed Al Nahyan, on Saturday morning, when he expressed his condolences following the death of the Queen, Downing Street said.
It comes after Ms Truss met Australian PM Anthony Albanese and New Zealand’s PM Jacinda Ardern at the Government’s Chevening country residence on Saturday.
The meetings were being framed by No 10 as chats, rather than formal bilateral sessions, with politics likely to feature.
In advance of her talks with Ms Truss, Ms Ardern said the Queen’s death and new King would be the “focus of conversationâ€, 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.â€
Mr Albanese also signed the condolence book at Lancaster House with his partner, Jodie Haydon, during his visit.
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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.â€