The World Health Organization chief pressed China on Thursday to share its information about the origins of COVID-19, saying that until that happened all hypotheses remained on the table, more than three years after the virus first emerged.
"Without full access to the information that China has, you cannot say this or that," said Director-General Tedros Adhanom Ghebreyesus in response to a question about the origin of the virus.
"All hypotheses are on the table. That's WHO's position and that's why we have been asking China to be cooperative on this."
"If they would do that then we will know what happened or how it started," he said.
The virus was first identified in the Chinese city of Wuhan in December 2019, with many suspecting it spread in a live animal market before fanning out around the world and killing nearly 7 million people.
Data from the early days of the COVID pandemic was briefly uploaded by Chinese scientists to an international database last month.
It included genetic sequences found in more than 1,000 environmental and animal samples taken in January 2020 at the Huanan seafood market in Wuhan, the location of the first known COVID outbreak.
The data showed that DNA from multiple animal species - including raccoon dogs - was present in environmental samples that tested positive for SARS-CoV-2, the virus that causes COVID, suggesting that they were "the most likely conduits" of the disease, according to a team of international researchers.
However, in a non-peer reviewed study published by the Nature journal this week, scientists with China's Center for Disease Control and Prevention have disputed the international team's findings.
They said the samples provided no proof the animals were actually infected. They were also taken a month after human-to-human transmission first occurred at the market, so even if they were COVID-positive, the animals could have caught the virus from humans.
The WHO's Maria Van Kerkhove, technical lead for COVID-19, said the latest Chinese information offered some "clues" on origins but no answers. She said the WHO was working with scientists to find out more about the earliest cases from 2019 such as the whereabouts of those infected.
She added WHO still did not know whether some of the research required had been undertaken in China.
The WHO has also asked the United States for original data that underpinned a recent study by the U.S. Energy Department that suggested a laboratory leak in China had likely caused the COVID-19 pandemic, she added.