The UK government called on the World Health Organisation to "explore all possible theories" around the origin of the coronavirus pandemic following reports that researchers at Wuhan's virology laboratory received hospital treatment in November 2019.
The leaked US intelligence report said three researchers from the Wuhan Institute of Virology (WIV) were so ill that they sought hospital care a month before China said the first patient was discovered in the central Chinese city with what became known as Covid-19.
The intelligence report, first leaked to the Wall Street Journal, has fuelled further debate about the origins of the coronavirus pandemic.
Asked about the report, the Prime Minister's official spokesman said: "The WHO investigation into the origins of the virus is ongoing and we have been clear throughout that it must be robust, transparent and independent.
"The investigation needs to explore all possible theories on how Covid-19 made that jump from animals to humans and how it spread and that's vital to ensure we learn lessons from this crisis and prevent another global pandemic."
Jen Psaki, the White House press secretary, said the Biden administration hoped the WHO could move into a more transparent investigation of the origins of the coronavirus pandemic.
However, she said the government could not confirm the intelligence report leaked to the Wall Street Journal: "We don't have enough data and information to come to a conclusion at this point in time."
The US intelligence report about the researchers' illness goes beyond the details released in a State Department fact sheet issued in the final days of Donald Trump's presidency.
The factsheet, released on January 19, stated that three researchers at the WIV, a lab for the research of coronaviruses and other pathogens, fell ill in the autumn of 2019 and had symptoms "consistent with both Covid-19 and other seasonal illnesses".
The leaked US intelligence report does not contain any further information on what illness the three researchers had.
The documents differ from a report filed by the Chinese government to the World Health Organisation, which stated the first patient with Covid-like symptoms was discovered in Wuhan on December 8, 2019.
The new details came as Dr Anthony Fauci, America's top infectious disease expert and the lead figure in the government's coronavirus response, said he was "not convinced" the virus developed naturally.
"I think we should continue to investigate what went on in China until we continue to find out to the best of our ability what happened."
According to the Wall Street Journal, officials familiar with the US intelligence had varying opinions on the strength of the information.
One individual told the newspaper that the report was provided by an international partner and needed further investigation. Another said the information "from various sources was of exquisite quality".
Authorities in China have strongly denied that the virus leaked from one of its labs.
"The US continues to hype the lab leak theory," China's foreign ministry said in response to The Wall Street Journal. "Is it actually concerned about tracing the source or trying to divert attention?"
"I've read it, it's a complete lie," said Yuan Zhiming, director of the Wuhan Institute of Virology, in response to the US report. "Those claims are groundless. The lab has not been aware of this situation, and I don't even know where such information came from."
A spokesperson at the virology lab said in response to a comment from the Telegraph: "Is there any necessary connection? It's also very normal for people to go to the hospital."
The Biden administration has declined to comment, stating all theories on the origin of the pandemic should be investigated by the World Health Organisation.
Last year, a WHO team travelled to Wuhan, the original epicentre, to investigate the origins of the virus.
In a joint report with Chinese experts, they concluded that the virus was most likely to have spread from bats to humans through another unknown animal and that a laboratory leak was "extremely unlikely".
At the time, experts revealed that while the first known case was detected on December 8, the virus was likely to have started spreading earlier.
On the same day the report was released, WHO chief Tedro Adhanom Ghebreyesus said that the team did not thoroughly examine the possibility of a lab leak.
China did not grant investigators access to raw data, original lab reports and other records at the Wuhan Institute of Virology.