Facing intensifying pressure for a new, more in-depth investigation of the Covid-19 pandemic origins, the World Health Organization said Friday that it was still awaiting expert guidance.

US President Joe Biden this week ordered the US intelligence community to investigate whether the Covid-19 virus first emerged in China from an animal source or from a laboratory accident.

The move hints at growing impatience with waiting for a conclusive WHO investigation into how the pandemic that has killed more than 3.5 million people worldwide began. 

The European Union and a range of other countries also pressed during an ongoing meeting of WHO member states for clarity on the next steps in its efforts to solve the mystery, seen as vital to averting future pandemics.

But the UN health agency said Friday it was still waiting for recommendations from a team of WHO technical experts on how to move forward.

"The technical team will prepare a proposal for the next studies that will need to be carried out and will present that to the director general," spokeswoman Fadela Chaib told reporters.

No timeline

"He will then work with member states about the next steps," she said, acknowledging "there is no timeline."

The WHO finally managed to send a team of independent, international experts to Wuhan in January, more than a year after Covid-19 first surfaced there in late 2019, to help probe the pandemic origins.

But in their long-delayed report published in late March, the international team and their Chinese counterparts drew no firm conclusions, instead ranking a number of hypotheses according to how likely they believe they were.

The report said the virus jumping from bats to humans via an intermediate animal was the most probable scenario, while a theory involving the virus leaking from a laboratory was "extremely unlikely".

But the investigation and report have faced criticism for lacking transparency and access, and for not evaluating the lab-leak theory more deeply -- a mere 440 words of the report were dedicated to discussing and dismissing it.

WHO chief Tedros Adhanom Ghebreyesus has also continued to insist that all theories remain on the table and further investigation is needed.

Long dismissed as a kooky right-wing conspiracy theory, and vehemently rejected by Beijing, the idea that Covid-19 emerged from a lab leak in Wuhan, China has been gaining increasing momentum in the United States.

While not suggesting that a lab leak was necessarily the source, a number of prominent international scientists have said a deeper, more scientific look at the theory was needed.

WHO believes that "further studies will be needed in a range of areas, including on the early detection of cases and clusters, and the potential roles of animal markets, transmission via the food chain and the laboratory incident hypothesis," Chaib said Friday.