The United States has sought more information from China as it has “deep concerns” about the early findings of the WHO expert investigation into the origins of the coronavirus in the country, national security advisor Jake Sullivan said on Saturday.

The statement came days after the WHO panel of inquiry returned from Wuhan in China, the believed point of origin of the pandemic, with no clear finding on the origin of the virus.

“We have deep concerns about the way in which the early findings of the COVID-19 investigation were communicated and questions about the process used to reach them,” Sullivan said.

“It is imperative that this report be independent, with expert findings free from intervention or alteration by the Chinese government,” he added.

Also read: China refuses to provide WHO with raw material on early COVID-19 cases: Report

Members of the WHO team had to walk a diplomatic tightrope during their stay, with the US urging a “robust” probe and China warning against politicizing the issue.

And he called on China to “make available its data from the earliest days of the outbreak.”

Peter Ben Embarek, the head of the inquiry panel, also voiced frustration on Saturday over the lack of access to raw data during the recent mission to China, saying more was needed to detect possible early COVID-19 cases.

“We want more data. We have asked for more data,” he told AFP in an interview.

The mission to Wuhan, where the first cases were spotted, failed to identify the source of the virus.

Also read: ‘All hypotheses still on the table’: WHO chief on COVID-19 origin

But it poured cold water on the theory backed by former US president Donald Trump that it leaked from a virology laboratory in the Chinese city, calling it “extremely unlikely”.

Beijing has repeatedly floated the theory that the virus was instead brought to China through packaging on products such as frozen seafood, a theory the WHO team did not rule out.

Experts believe the disease originated in bats and could have been transmitted to humans via another mammal.

Sullivan backed the WHO and expressed “deep respect” for the agency, which the US under President Joe Biden is rejoining. The Trump administration moved to quit it, saying in July 2020 that the agency was under China’s complete influence and had produced an ineffectual virus response.

But Sullivan also clarified that “re-engaging the WHO also means holding it to the highest standards. And at this critical moment, protecting the WHO’s credibility is a paramount priority.”

Since the virus emerged in China in December 2019, it has killed at least 2,384,059 people worldwide, according to a tally from official sources compiled by AFP at 1100 GMT on Saturday.