The World Health Organization said Monday that Washington had not provided evidence to support "speculative" claims by the U.S. President that the new coronavirus originated in a Chinese laboratory.
"We have not received any specific data or evidence from the United States government regarding the alleged origin of the virus – so from our perspective, this remains speculative," said Michael Ryan, WHO's emergency director, in a virtual briefing.
Scientists believe the killer virus jumped from animals to humans, emerging in China at the end of last year, possibly from a market in Wuhan that sells exotic animals for meat.
Leading U.S. epidemiologist Anthony Fauci repeated the WHO statement in an interview published Monday night by National Geographic.
"If you look at the evolution of the virus in bats and what's out there now, (the scientific evidence) is very, very strongly inclined to it, it could not have been artificially or deliberately manipulated," Fauci told the magazine.
"Everything about gradual evolution over time strongly indicates that (this virus) evolved in the wild and then jumped species," he said.
U.S. President Donald Trump, increasingly critical of China's outbreak management, claims to have evidence that it started in a Wuhan laboratory.
And U.S. Secretary of State Mike Pompeo said on Sunday that "huge evidence" supported this claim, although the U.S. intelligence community last week said it would continue to study whether the outbreak resulted from contact with infected animals or a laboratory accident.
China vehemently denied suggestions that the laboratory was the source.
"Like any evidence-based organization, we would be very willing to receive any information regarding the origin of the virus," said Ryan, emphasizing that this was "a very important piece of public health information for future control."
"If this data and evidence is available, it will be for the United States government to decide if and when it can be shared, but it is difficult for WHO to operate in the information vacuum in this regard," he added.
– Science at the center –
The UN health agency – which also faced sharp criticism from Trump over allegations that it initially minimized the severity of the outbreak to protect China – repeatedly said the virus clearly appears to have originated naturally from an animal source.
WHO expert Maria Van Kerkhove emphasized during Monday's briefing that there were about 15,000 complete genome sequences of the new coronavirus available and "from all the evidence we've seen … this virus is of natural origin".
Although coronaviruses often originate from bats, Van Kerkhove and Ryan emphasized the importance of finding out how the virus that causes COVID-19 passed on to humans and which animal served as an "intermediate host" along the way.
"We need to understand more about this natural origin, and particularly about intermediate hosts," said Ryan.
It was important to know "so that we can implement the right public health policies and animal-human interface that will prevent this from happening again," he emphasized.
WHO said last week that it wanted to be invited to participate in Chinese investigations into the animal origins of the pandemic, which in a matter of months killed more than 250,000 people worldwide.
"We offer, as in all cases in all countries, assistance in carrying out these investigations," said Ryan on Monday.
"We can learn from Chinese scientists," he said.
But he warned that if the questions about the virus's origin were "designed as an aggressive investigation of irregularities, I think it is much more difficult to deal with. This is a political issue.
"Science needs to be at the center," he said.
"If we have a scientific investigation and a scientific investigation of what are the species of origin and the intermediate species, that will benefit everyone on the planet".