But defending the W.H.O. on Wednesday, Dr. Michael Ryan, the executive director of its emergencies programs, cited the early warning it sounded.
“We alerted the world on January the Fifth,” Mr. Ryan told reporters.
Dr. Ghebreyesus expressed disappointment with Mr. Trump’s decision to freeze funding.
“W.H.O. is not only fighting Covid-19,” he said. “We’re also working to address polio, measles, malaria, Ebola, H.I.V., tuberculosis, malnutrition, cancer, diabetes, mental health and many other diseases and conditions.”
Mr. Trump’s decision to attack the W.H.O. comes as he is under intense fire at home for a failure to respond aggressively to the virus, which as of Wednesday had claimed more than 28,000 lives and infected at least 600,000 people in the United States.
The president publicly shrugged off the virus throughout January and much of February, repeatedly saying that it was under control. He said in mid-February that he hoped the virus would “miraculously” disappear when the weather turned warm.
Mr. Trump barred some travel from China in late January, a move that health experts say helped delay widespread infection. But he also presided over a government that failed to make testing and medical supplies widely available and resisted calling for social distancing that allowed the virus to spread for several critical weeks.
The president’s decision to freeze the W.H.O. funding was backed by many of his closest aides, including Peter Navarro, his trade adviser, and key members of the National Security Council, who have long been suspicious of China. Mr. Trump himself has often offered contradictory messages about the country — repeatedly saying nice things about Mr. Xi even as he wages a fierce, on-again, off-again trade war with China.