Geneva, Switzerland - The World Health Organization chief said Tuesday that operations and jobs would be slashed as US funding cuts had left the UN agency with a budget hole of several hundred million dollars.

"The sudden drop in income has left us with a large salary gap and no choice but to reduce the scale of our work and workforce," Tedros Adhanom Ghebreyesus told member states, according to a transcript of his remarks.

The United Nations health agency has been bracing for President Donald Trump's planned full withdrawal of the US – by far its largest donor – next January.

The US gave WHO $1.3 billion for its 2022-2023 budget, mainly through voluntary contributions for specific projects rather than fixed membership fees.

But Washington never paid its 2024 dues, and is not expected to pay its 2025 dues.

This has left the WHO preparing a new structure, which Tedros presented to staff and member states on Tuesday.

"The refusal of the US to pay its assessed contributions for 2024 and 2025, combined with reductions in official development assistance by some other countries, means we are facing a salary gap for the 2026–27 biennium of between $560 and $650 million," he said.

The lower end of that spectrum "represents about 25% of staff costs" currently, he said, stressing that "that doesn't necessarily mean a 25% cut to the number of positions."

He did not say how many jobs would be lost at the WHO, which employs more than 8,000 people around the world.

Tedros insisted that the most significant impact would likely be felt at the organisation's headquarters in Geneva. "We are starting with reductions in senior management," he said.

WHO's regional offices would meanwhile be affected "to varying degrees," he said, adding that some country offices in wealthier countries would likely be closed.