Making the UN "fit for purpose" will dominate Donald Trump's first day at his debut General Assembly in New York.
Trump chose UN reform as the theme of the traditional US-hosted event that takes place every year before speeches begin on Tuesday.
He will be joined by his UN ambassador Nikki Haley and Secretary General Antonio Guterres, as well as leaders from 120 countries who have signed a communique in support of the UN chief's reform agenda.
A draft of the document includes a key point urging "greater transparency and predictability on required resources" and urges Guterres to "initiate effective, meaningful reform to make the United Nations fit for purpose."
Guterres, who took over from Ban Ki-Moon as head of the UN in January, campaigned for the role on a platform of reforming the organisation.
Vice President Mike Pence and Secretary of State Rex Tillerson are also joining Trump for the General Assembly at the UN's New York headquarters.
The US President has accused the UN of being a "club for people to get together, talk and have a good time" and said spending is "out of control."
In his budget proposal earlier this year, he threatened to slash roughly $US1 billion from the peacekeeping fund, which Guterres said would make the UN's work impossible.
The US is the biggest contributor to the organisation, and pays 25 per cent of the general budget and 28 per cent towards peacekeeping funds.
