The head of the World Health Organization (WHO) has said further investigation is needed to conclusively rule out that Covid-19 emerged from a laboratory in China.
Tedros Adhanom Ghebreyesus said that although a lab leak was the least likely cause, more research was needed.
The US and other countries have criticised China for failing to provide the WHO with sufficient data.
Beijing has always dismissed the allegations of a virus leak.
A report by WHO and Chinese experts released on Tuesday, said the lab leak explanation was highly unlikely and the virus had probably jumped from bats to humans via another intermediary animal.
China has yet to respond to the WHO’s latest statement.
‘All hypothesis on the table’
However the theory that the virus might have come from a leak in a laboratory “requires further investigation, potential with additional missions involving specialist experts,” Dr Tedros said on Tuesday.
“Let me say clearly that as far as WHO is concerned, all hypothesis remain on the table,” he added.
The virus was first detected in Wuhan, in China’s Hubei province in late 2019. An international team of experts travelled to to the city in January to probe the origins of the virus.
Their research relied on samples and evidence provided by Chinese officials but Dr Tedros said the team had difficulty accessing raw data and called for “more timely and comprehensive data sharing” in the future.
The team investigated all possibilities, including one theory that the virus had originated at the Wuhan Institute of Virology. The institute is the world’s leading authority on the collection, storage and study of bat coronaviruses.
In response to the WHO report, the US and 13 allies including South Korea, Australia and the UK voiced concern over the findings and urged China to provide “full access” to experts.
The statement said the mission to Wuhan was “significantly delayed and lacked access to complete, original data and samples”.
“Scientific missions like these should be able to do their work under conditions that produce independent and objective recommendations and findings.”
The group pledged to work together with the WHO.
Former US President Donald Trump was among those who supported the theory that the virus might have escaped from a lab.
WHO investigation team leader, Peter Ben Embarek said on Tuesday his team had felt under political pressure, including from outside China but said he was never pressed to remove anything from the team’s final report.
He also confirmed his team had found no evidence that any laboratories in Wuhan were involved in the outbreak.
Dr Embarak also said that it was “perfectly possible” that cases were circulating in the Wuhan area in October or November 2019. China informed the WHO about cases on 3 January, a month after the first reported infection.
China has always rejected claims the virus originated in a lab and says that although Wuhan is where the first cluster of cases was detected, it is not necessarily where the virus originated.
State media has claimed that the virus may have arrived in Wuhan on frozen food imports.
The country has largely brought its own outbreak under control through quick mass testing, stringent lockdowns and tight travel restrictions.
Worldwide, more than 127 million people have caught the virus since it was first identified, and more than 2.7 million people are known to have died from it.