It also lent credence to a theory that the virus may have emerged from a Chinese research laboratory instead of in nature.

China's embassy in the United States said on 27 May that politicising the issue would hamper investigations into the origins of Covid-19.

China supports "a comprehensive study of all early cases of Covid-19 found worldwide and a thorough investigation into some secretive bases and biological laboratories all over the world," the embassy said in remarks attributed to a spokesperson, posted on its website.

China's embassy in the United States said that politicising the issue would hamper investigations into the origins of Covid-19

The origin of the virus remains contested among experts. The first known cases emerged in the central Chinese city of Wuhan in December 2019.

In a report issued in March and written jointly with Chinese scientists, a World Health Organization-led team that spent four weeks in and around Wuhan in January and February said the virus had probably been transmitted from bats to humans through another animal, and that "introduction through a laboratory incident was considered to be an extremely unlikely pathway."

Specific questions for China

Washington's frustration has mounted in recent weeks over what it sees as insufficient cooperation from China into the international investigation.

"I have now asked the Intelligence Community to redouble their efforts to collect and analyze information that could bring us closer to a definitive conclusion, and to report back to me in 90 days," Biden said.

"As part of that report, I have asked for areas of further inquiry that may be required, including specific questions for China."

US agencies have been pursuing Covid-19's origins since the government first recognised the virus as a serious health risk in early 2020.

Earlier this week, the US government sources said a still-classified US intelligence report circulated during former president Donald Trump's administration alleged that three researchers at China's Wuhan Institute of Virology became so ill in November 2019 that they sought hospital care.


The source of that early intelligence or how reliable US agencies rate it is not known. It remains unclear whether the afflicted researchers were hospitalised or what their symptoms were, one of the sources said.

Intelligence committees of both the US Senate and House of Representatives are investigating how US agencies have reported on and gathered information about Covid-19's origin, how it spread and how governments have responded to it.

A report issued by House Intelligence Committee Republicans earlier this month focused particularly on the Wuhan Institute of Virology.

The Republican report asserted that "significant circumstantial evidence raises serious concerns that the Covid-19 outbreak may have been a leak" from the institute, suggested the Wuhan lab was involved in biological weapons research, and that Beijing had attempted to "cover up" the virus' origins.

Washington has called for the WHO to open a second phase to its investigation on COVID-19's origin.

On 26 May in Geneva, WHO emergency director Mike Ryan said the agency expected to provide an update on its proposed next steps "in the coming weeks."

China's delegation to the WHO said on 25 May it was calling on "all parties" to "adopt an open and transparent attitude" to cooperate with the WHO's attempts to trace the virus' origin.

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