But to go further, the team needs "full access to data including biological samples from at least September 2019", Dr Tedros said.
Director-general Tedros Adhanom Ghebreyesus also said a World Health Organization team looking for the source of the virus had encountered problems accessing raw data, and called for further studies because the assessment so far has not been extensive enough.
All hypotheses into the origins of the virus "remain on the table" and "no stone will be left unturned", the World Health Organization said as it continues its probe into where the virus came from.
He said the report was a "very important beginning" but not the end.
The countries expressed support for the WHO's experts and staff, citing their "tireless" work toward ending the pandemic and understanding its origins to help prevent a future one.
The report, a copy of which was seen by the Telegraph earlier this week, concluded that the theory that the virus escaped from a laboratory, while possible, is "extremely unlikely".
However, Dr Tedros said the team's assessment was "not extensive enough".
During the visit to Wuhan, Chinese officials refused to share raw data about some of the earliest possible virus cases with the World Health Organization team, frustrating some of the visiting scientists. "The possible intermediate host of SARS-CoV-2 remains elusive", the report reads.
It also said the role played by a seafood market where human cases were first identified was uncertain.
Looking at available data, the report suggests there was unrecognised transmission in December 2019, and possibly earlier. "And I think this report is a testament to how, even under very intense scrutiny and very hard political circumstances, countries can come together to focus on the origins of emerging diseases", Daszak said.
Separately, in what it called a joint statement by 14 countries, the State Department said they were calling for "momentum" for a second-phase look by experts and pointed to the need for further animal studies "to find the means of introduction into humans" of the coronavirus.
And so far, tests of a wide range of domestic and wild animals in the region where the outbreak first started have shown no evidence of SARS-CoV-2.
But the investigation has not found what other animal was infected by a bat - considered the most likely original source of the virus - and then may have transmitted it to a human.
A spillover from bats via another animal is the most likely scenario in the report, followed by direct spillover.
China's official explanation maintains that the Huanan live food market in Wuhan - an early hotbed of infections - may have been exposed to the virus through channels including cold chain foods and animal products from other parts of the world.
Mark Woolhouse, an epidemiologist at the University of Edinburgh, said even that "very low probability" was an overstatement.
Highly similar viruses have also been found in pangolins, suggesting cross-species transmission from bats at least once.
Rasmussen agrees. "A team of scientists is not qualified to conduct a detailed audit of WIV's records, or get access to institutional files, lab notebooks, databases, or freezer inventories", she says.
The WHO's investigation into the origins of the virus has been the subject of intense investigation and criticism.
A statement released by the governments of the United States, Australia, Canada, Czechia, Denmark Estonia, Israel, Japan, Latvia, Lithuania, Norway, the Republic of Korea, Slovenia and the U.K. also voiced concern about the report.
White House press secretary Jen Psaki said experts from seven different U.S. government organisations including the Centers for Disease Control and Prevention, the National Institute of Health and the Department of Homeland Security had the report in hand.
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