A Sunday report from the Sunday Times of London quotes British spies who initially dismissed the lab leak theory, but now say it is "feasible."
"There might be pockets of evidence that take us one way, and evidence that takes us another way," the paper quoted a source as saying. "The Chinese will lie either way. I don’t think we will ever know."
The quote comes as both the United States and Britain are stepping up calls for the World Health Organization to take a deeper look into the possible origins of COVID-19, including a new visit to China, where the first human infections were detected.
WHO and Chinese experts issued a first report in March that laid out four hypotheses about how the pandemic might have emerged. The joint team said the most likely scenario was that the coronavirus jumped into people from bats via an intermediary animal, and the prospect that it erupted from a laboratory was deemed "extremely unlikely."
The Biden administration wants to step up calls for China to be more open about the outbreak, aiming to head off complaints from opposition Republican senators that the president has not been tough enough, as well as to use the opportunity to press China on alleged obstruction.
Republicans, including former President Donald Trump, have promoted the theory that the virus emerged from a laboratory accident rather than naturally through human contact with an infected animal in China.
During an interview with CBS’ ‘Face The Nation’ on Sunday, former Food and Drug Administration Commissioner Scott Gottlieb said accidental lab leaks "happen all the time."
"These kinds of lab leaks happen all the time, actually," Gottlieb said. "Even here in the United States, we’ve had mishaps, and in China, the last six known outbreaks of SARS-1 have been out of labs, including the last known outbreak, which was a pretty extensive outbreak that China initially wouldn’t disclose that it came out of a lab."
And earlier this month the Wall Street Journal reported that three researchers at the Wuhan Institute of Virology in late 2019 displayed symptoms consistent with COVID-19 and required hospital treatment.
President Biden, meanwhile, said the intelligence community has yet to determine whether the pandemic began after human contact with infected animals or because of a lab accident. Officials are expected to deliver an updated report on their conclusion within the next few months.
Fox News’ Thomas Barrabi and the Associated Press contributed to this report.