A US intelligence report requested by President Biden into the origins of the coronavirus pandemic is inconclusive, US media reports say.
Agencies are reportedly divided on whether the virus - first seen in China - was the result of a natural spillover from animals to humans or was caused by a laboratory accident, reports BBC.
An summary of the report is expected to be published in the coming days.
China's foreign minister has dismissed the report as "anti-science".
Wang Yi said Washington had "ignored and abandoned" research carried out by the World Health Organization (WHO) for a report that would only service its "political purposes".
The pandemic, which has claimed more than four million lives around the world, began in the Chinese city of Wuhan in early 2020.
While countries have been working to contain the spread of Covid-19, scientists have been trying to work out where the virus originated.
A WHO team, which visited Wuhan, concluded in a report earlier this year that the disease most likely spilled over from an animal sold at a market.
The report appears to dismiss the possibility that the virus might have leaked accidentally from the Wuhan Institute of Virology, which has studied coronaviruses in bats for more than a decade.
This conclusion has been rejected by some scientists.
In May President Biden gave the US intelligence agencies 90 days to assess the data and produce a report that "could bring us closer to a definitive conclusion" on the origins of the virus.
Intelligence that several researchers at the Wuhan lab were hospitalised in November 2019, and China's refusal to allow a thorough investigation into the lab theory, are said to have prompted Mr Biden's decision.
However, in June, Director of National Intelligence Avril Haines played down hopes of reaching a conclusion, telling Yahoo News: "We're hoping to find a smoking gun, but it might not happen."
Many scientists believe it could take years of research before a definitive conclusion on the virus's origins is reached.
"We should not even be thinking about closing the book or backing off, but rather ratcheting up the effort," David Relman, a Stanford University microbiologist, told the Washington Post.
China meanwhile has been stoking the idea that virus originated from Fort Detrick, a military installation in the US. The facility was once the centre of the US biological weapons programme and currently houses biomedical labs researching viruses including Ebola and smallpox.
Foreign Ministry spokesman Wang Wenbin referred to it again on Wednesday saying the US "should start with inviting WHO experts to launch a probe into Fort Detrick".
The US intelligence report was delivered to President Biden on Monday. White House spokeswoman Jen Psaki said it might take "a couple of days, if not longer, to put together an unclassified version" for the public.