Australia has joined the United States, Great Britain, Japan and the European Union in calling for international experts to be allowed to evaluate the source of the coronavirus, after an international mission to China earlier this year proved inconclusive..

US intelligence agencies are examining reports that researchers at a Chinese virology laboratory were seriously ill in 2019 a month before the first cases of COVID-19 were reported, according to US government sources who cautioned on Monday that there is still no proof the disease originated at the lab.

“Phase 2 of the COVID origins study must be launched with terms of reference that are transparent, science-based, and give international experts the independence to fully assess the source of the virus and the early days of the outbreak,” US health secretary Xavier Becerra said in a video message to the annual ministerial meeting of the World Health Organisation.

Addressing the World Health Organisation’s (WHO) main annual meeting of member states, representatives from several countries stressed the continued need to solve the mystery of how COVID-19 first began spreading among humans.

“We underscore the importance of a robust comprehensive and expert-led inquiry into the origins of COVID-19,” US representative Jeremy Konyndyk told the World Health Assembly (WHA).

Australia, the European Union and Japan were among others to call for more progress on the investigation, while the British representative urged that any probe be “timely, expert-driven and grounded in robust science”.

Mr Becerra did not mention China directly, where the first known human cases of COVID-19 emerged in the central city of Wuhan in December 2019.

The origin of the virus that causes COVID-19 is hotly contested.

Determining how the virus began spreading is seen as vital to preventing future pandemics.

In a report issued in March written jointly with Chinese scientists, a WHO-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”.

Top US infectious disease expert Dr Anthony Fauci has urged caution over claims the virus was man-made.

At a virtual event hosted by Poynter Institute on May 11, Dr Fauci was asked whether he was convinced with the theory that the virus “developed naturally.”

“I am not convinced…I think we should continue to investigate what went on in China until we find out to the best of our ability exactly what happened,” Dr Fauci said.

A WHO spokesman, Tarik Jasarevic, asking about a follow-up mission, told Reuters on Monday that the agency was reviewing the recommendations from the report at the technical level.

“The technical teams will prepare a proposal for the next studies that will need to be carried out, and will present that to the Director-General for his consideration,” he said, referring to WHO director-general Tedros Adhanom Ghebreyesus.

Mr Jasarevic, noting Mr Tedros’ remarks on March 30, said that further studies would be needed in a range of areas, including on the early detection of cases and clusters, the potential roles of animal markets, transmission via the food chain and the laboratory incident hypothesis.

-with agencies