The World Health Organization will cut costs and review which health programmes to prioritise after President Donald Trump announced he was withdrawing the U.S. from the WHO, the agency's chief told staff in an internal memo seen by Reuters.

Trump made the move on the first day of his second term in office on Monday, accusing the U.N. health agency of mishandling the COVID-19 pandemic and other international health crises.

"This announcement has made our financial situation more acute...," WHO Director-General Tedros Adhanom Ghebreyesus said in the memo dated Jan. 23. It said the WHO planned to significantly reduce travel expenditure and halt recruitment, except for critical areas, as part of cost-saving measures.

A WHO spokesperson confirmed the memo - first reported by Reuters - was authentic but declined to comment further.

The United Nations confirmed on Thursday that the United States was due to withdraw from the WHO on Jan. 22, 2026, after a one-year notice period required under a 1948 joint resolution of the U.S. Congress. The resolution also states that Washington must pay its dues to the WHO before exiting.

The United States is by far the WHO's biggest financial backer, contributing around 18% of its overall funding. WHO's most recent two-year budget, for 2024-2025, was $6.8 billion.

The U.S. already owes the WHO around $130 million in membership fees that were due a year ago, in January 2024, WHO spokesperson Christian Lindmeier told a U.N. briefing in Geneva on Friday, although he said such a delay was not unusual.

"We also have not received the 2025 assessment, the membership fee, which would have been due now," he added. The U.S. contribution to WHO also includes voluntary fees, earmarked for certain programmes, and those payments could be stopped at any time, he added.

The memo said the WHO had already worked to reform the organization and change how it is funded, with member states increasing their mandatory fees and contributing to its investment round launched last year.

But it said more funding would be needed and costs would have to be cut simultaneously. This would include making all meetings virtual by default without exceptional approval, limiting the replacement of IT equipment, and suspending office refurbishments unless linked to safety or already approved cost-cutting.

"This set of measures is not comprehensive, and more will be announced in due course," the memo reads, adding that the Geneva-based WHO would do everything it could to support and protect staff.

"As always, you make me proud to be WHO," the memo ends.