United Nations (United States) (AFP) - US President Donald Trump will host a meeting of world leaders at the United Nations this month to push for reform of the global body that he once dismissed as a "club" for people "to have a good time."

World leaders at the September 18 event will be asked to support a 10-point political declaration that backs UN Secretary-General Antonio Guterres "in making concrete changes to the United Nations," according to the document obtained by AFP on Friday.

Attending his first UN gathering of world leaders, Trump is scheduled to address the General Assembly on September 19, on the first day of the six-day debate.

His speech will likely to be the most closely watched as Washington's allies and foes grapple with the implications of his "America-First" approach to foreign policy.

Trump has described the United Nations as an "underperformer" but stressed that it has "huge potential" to address the long list of world crises that will be at the center of this year's UN debate.

The United States is the UN's number one financial contributor, paying 28.5 per cent of the $7.3 billion peacekeeping budget and 22 per cent of the core budget of $5.4 billion.

The Trump administration has threatened to cut billions in funding to the world body while US Ambassador Nikki Haley was a driving force behind a $600 million-cut to the UN peacekeeping budget this year.

To push for reform, the United States has enlisted support from 14 other countries: Britain, Canada, China, Germany, India, Indonesia, Japan, Jordan, Niger, Rwanda, Senegal, Slovakia, Thailand and Uruguay.

The 14 countries will co-host the event at UN headquarters that will feature an address from Trump, Haley and Guterres, diplomats said.

In the declaration, countries will "commit to reducing mandate duplication, redundancy, and overlap including among the main organs of the United Nations."

They encourage Guterres to "pursue impactful and field-centric management reforms," the document said.

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Guterres, a former prime minister of Portugal, is pushing for sweeping reforms that touch management at the United Nations as well as its development agencies and its peace and security architecture.

His proposals are to be debated at the assembly in the coming weeks.

The declaration on UN reform is not binding, but reflects political support for changes at the world body, diplomats said.