Records of early Covid-19 cases in Wuhan were deleted from a US database at the request of Chinese scientists, American officials have confirmed.

A team of academics from Wuhan, where the first documented cases of Covid-19 appeared, submitted sequences of the virus that causes the disease to a US-based archive in March 2020.

Three months later, however, they asked for those sequences to be removed and the data were deleted, the US National Institutes of Health said on Wednesday, confirming the results of an investigation by biologist Jesse Bloom.

“Submitting investigators hold the rights to their data and can request withdrawal of the data,” NIH said in a statement.

The deleted information did not prove how Covid-19 first infected humans, whether via animals or a laboratory leak from the Wuhan Institute of Virology. But experts said the incident demonstrated further evidence of how Chinese researchers and officials have not been fully transparent in how they dealt with data related to the pandemic’s origins.

Richard Ebright, a professor of chemical biology at Rutgers University, said: “The findings do not shed direct light on the issue of origins. The results do not rule out a natural-spillover origin and do not rule in a laboratory-spillover origin.”

But he added: “[They do] provide evidence of deliberate obfuscation of early events in the emergence of Sars-Cov-2 in Wuhan in fall 2019 and evidence of deliberate obstruction of the investigation of those events.”

Scientists have been trying to work out how the pandemic began in order to prevent a future outbreak. But while most believe the virus crossed over to humans from animals, they have been unable to identify which animal was responsible for conveying the virus from bats.

Donald Trump, the former US president, has promoted unproven theories that the virus leaked from the Wuhan lab, one of the world’s leading centres of research on bat coronaviruses. China has denied the allegation, but the theory has gained traction again in recent weeks, with US president Joe Biden ordering intelligence officials to “redouble” efforts to investigate the origins of the pandemic and come to their own conclusions.

Much of the research into the early stages of Covid-19 has focused on virus samples taken from patients in Wuhan early last year and investigated by a team convened by the World Health Organization. That investigative team found it was “extremely unlikely” the virus had leaked from a research lab, but the WHO itself has said the investigation had not been extensive enough.

According to Bloom, a virologist at the Fred Hutchinson Cancer Research Center in Seattle, other sequences of the virus’ genome exist, taken from patients in Wuhan in January and February 2020 as part of an attempt by researchers at Wuhan University to improve testing for the disease.

Those samples were logged with the NIH, but did not appear when Bloom looked for them as part of his own investigation into how the pandemic started.

Bloom managed to retrieve most of the data, however, after realising it had not been deleted from Google Cloud. The missing sequences, he said, did not prove any of the theories around Covid-19’s origins, but did suggest the virus had been circulating in Wuhan for longer than Chinese authorities have admitted.

Wuhan University did not respond to a request for comment.