WHO director-general Tedros Adhanom Ghebreyesus said on Friday that "I have written to and spoken with high-level Chinese leaders on multiple occasions as recently as just a few weeks ago... all hypotheses on the origins of the virus remain on the table."

Earlier this week, FBI Director Christopher Wray told Fox News that "the FBI has for quite some time now assessed that the origins of the pandemic are most likely a potential lab incident in Wuhan."

Mr Wray said that the Chinese government was "doing its best to try to thwart and obfuscate" efforts by the US and others to learn more about the pandemic's origins.

The US Energy Department has also concluded the lab leak theory is credible. In a report circulated to the White House and members of Congress, the department said it had "low confidence in its judgement; the FBI said it had "moderate confidence" in its verdict.

WHO's official position, taken from a 2021 report, said the most likely explanation was that the virus originated in a bat before crossing to an intermediary animal then jumping to humans, but has not ruled out the lab leak theory and continues to investigate.

"I wish to be very clear that WHO has not abandoned any plans to identify the origins of the COVID-19 pandemic," Dr Tedros said.

The FBI won't disclose details of the information they had access to, which has caused some frustration to some at WHO. Maria Van Kerkhove, the body's technical lead on COVID-19, urged any organisation that had information on the origins of the pandemic to share it.

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"I am deeply frustrated at the lack of additional information from the US reports assessing COVID-19 origins, which have not been shared with us and from investigations in China that can actually further the technical, serious discussions.

"We don't completely have the answers to how this pandemic began and it remains absolutely critical that we continue to focus on this," she said.

"Our work continues on this space: looking at studies in humans, looking at studies in animals, looking at studies at the animal human interface, and also looking at potential breaches in biosafety and biosecurity for any of the labs that were working with coronaviruses, particularly where the first cases were detected in Wuhan, China, or elsewhere."