A UN conference aiming to rally fresh support for development aid begins in Spain on Monday with the sector in crisis as US-led funding cuts jeopardise the fight against poverty.

At least 50 world leaders, including French President Emmanuel Macron, Kenya's William Ruto, EU chief Ursula von der Leyen and UN head Antonio Guterres will gather in the city of Seville from June 30 to July 3.

But key player the United States is snubbing the biggest such talks in a decade, underlining the erosion of international cooperation on combating hunger, disease and climate change.

South African President Cyril Ramaphosa, whose country has tried to promote Global South priorities such as debt during its presidency of the G20 club of wealthy nations, cancelled his visit amid domestic political tensions.

More than 4,000 representatives from businesses, civil society and financial institutions will also attend the Fourth International Conference on Financing for Development.

UN sustainable development goals set for 2030 are slipping from reach just as the world's wealthiest countries are withdrawing funding for development programmes.

Reforming financial system

President Donald Trump's gutting of the US development agency USAID is the standout example, with Germany, Britain and France among other rich economies making cuts when faced with competing priorities such as defence.

International charity Oxfam says the cuts to development aid are the largest since 1960 and the United Nations puts the growing gap in annual development finance at $4 trillion.

More than 800 million people live on less than $3 per day globally, according to the World Bank, with rising extreme poverty affecting sub-Saharan Africa in particular.

Disruption to global trade from Trump's tariffs and ongoing conflicts in the Middle East and Ukraine have dealt further blows to the diplomatic cohesion necessary for concentrating efforts on helping countries escape poverty.

Among the key topics up for discussion is reforming international finance to help poorer countries shrug off a growing debt burden that inhibits their capacity to achieve progress in health and education.

The total external debt of the group of least developed countries has more than tripled in 15 years, according to UN data.