STORY: U.S. President Donald Trump is pulling the U.S. out of the World Health Organization.

And that's raised concerns about the U.N. agency's ability to fight diseases and respond to emergencies around the globe.

And it raises questions about funding for the agency in its mission.

:: Biggest donor

The main reason for that is that the U.S. is the WHO's biggest donor.

It contributes about 18% of its funding. The agency's two-year budget for 2024-2025 was $6.8 billion.

Data from WHO show that, in that period, the U.S. financed 75% the agency's program treating HIV and other sexually transmitted diseases.

It also provided over half of the contributions to combat tuberculosis - the world's biggest infectious disease killer.

Trump's withdrawal is coming at a time when the WHO is struggling to raise cash for health emergencies from Gaza to Ukraine.

:: Pandemic treaty

Trump is also skeptical about WHO-led negotiations for a post-COVID pandemic agreement aimed at improving global solidarity when the next health threat strikes.

Billionaire Trump ally Elon Musk has said nations should not "cede authority" to the WHO.

The U.S. will cease negotiations on the treaty while its withdrawal proceeds.

In addition, the U.S. is part of a global influenza surveillance network supervised by the UN agency.

:: How has the WHO responded?

"We hope the United States will reconsider."

The WHO says it plays a crucial role in the protecting the health and security of the world's people, including Americans.

:: Tarik Jasarevic, WHO Spokesperson

:: Geneva, Switzerland

"It's too early to say what are the consequences. We need really to look into it, what are the implications, but we will continue our work in trying really to get that funding that we need."

The European Union said it was concerned by Trump's decision, and called on all WHO member states to address the financial challenge now presented.

China's foreign ministry said the WHO's role in global health should be strengthened, not weakened, and

promised to continue Beijing's support.