More than 14 million of the world's most vulnerable people, a third of them small children, could die because of the Trump administration's dismantling of US foreign aid, research projected on Tuesday.

The study in the prestigious Lancet journal was published as world and business leaders gather for a UN conference in Spain this week hoping to bolster the reeling aid sector.

The US Agency for International Development (USAID) had provided over 40 percent of global humanitarian funding until Donald Trump returned to the White House in January.

Two weeks later, Trump's then-close advisor -- and world's richest man -- Elon Musk boasted of having put the agency "through the woodchipper".