The World Health Organization said Friday it was reviewing its priorities in preparation for the withdrawal of its largest donor, the U.S., and stressed that it provides vital services that protect the country from health threats. President Trump on Monday signed an executive order directing the U.S. to withdraw from the WHO, a body he has repeatedly criticized over its handling of the COVID-19 pandemic.

“This announcement has made our financial situation more acute, and we know it has created significant concern and uncertainty for the WHO workforce,” the organization’s chief Tedros Adhanom Ghebreyesus said in a letter sent to WHO staff Thursday and seen by AFP on Friday.

He stressed that the United Nations’ health agency regretted the decision by the leader of the U.S. — by far the agency’s biggest donor — and hoped “the new administration will reconsider it.”