The head of the World Health Organization (WHO) has met the Chinese premier for talks on COVID-19, including on the stalled investigation into the pandemic’s origins.

The meeting between Tedros Adhanom Ghebreyesus and Li Keqiang on Saturday came as the issue of the origin of the coronavirus strained relations between China and the West.

The WHO director-general, visiting Beijing for the 2022 Winter Olympics, posted a picture on Twitter of the pair sitting with officials in a meeting room. Ghebreyesus has previously pressed China to be more forthcoming with data and information related to the origin of the virus.

“Pleased to meet with Premier Li Keqiang,” Tedros tweeted on Saturday. “We discussed COVID-19 and the need for an aggressive effort on VaccinEquity this year to vaccinate 70 percent of all populations,” he said, referring to the WHO campaign for fair access to vaccines around the world.

Where, when and how the virus originated remains one of the central mysteries of COVID-19, which has killed more than six million people worldwide. The United States and other countries have criticised China for delaying sharing information when the virus emerged there in 2019.

In December, the WHO said Beijing had still not disclosed some early data that might help pinpoint the origins and called for a second phase of an investigation into it.

‘Lab leak cannot be ruled out’

Jeremy Farrar, director of the Wellcome Trust who quit as a UK government adviser in November, said earlier in the week that the “overwhelming majority” of evidence points towards natural origins, although a laboratory leak still cannot be ruled out.

Without international cooperation, finding out more may be impossible, alongside establishing which other animal viruses might pose a risk to humanity.

The WHO established last year the Scientific Advisory Group on the Origins of Novel Pathogens (SAGO) and called on China to supply raw data to help any new investigation. China declined, citing patient privacy rules.

China has consistently denied allegations that the virus was leaked from a specialist laboratory in the city of Wuhan, where COVID-19 was first identified at the end of 2019.

A joint study by China and the WHO published last year all but ruled out the theory that COVID-19 originated in a laboratory, saying that the most likely hypothesis was that it infected humans naturally, probably via the wildlife trade.

Last November, China said a declassified US intelligence report saying it was plausible that the pandemic originated in a laboratory was unscientific and had no credibility.