Donald Trump's officials are spending the final days of his presidency ramping up accusations China covered up the existence of Covid-19.
His administration claims it will release intelligence reports in days that it says contain evidence Wuhan researchers fell ill with Covid-19-like symptoms long before the world knew of the virus.
The US has so far stopped short of backing a widespread conspiracy theory that the virus leaked from the Wuhan Institute of Virology.
The UK has also declined to speculate, but called for China to assist investigators searching for answers.
Beijing has repeatedly denied the theories, saying the outbreak began in the city at the end of December 2019.
It has faced international criticism for frustrating attempts to investigate the origin of the pandemic.
The World Health Organisation (WHO) just last week landed a research team in China, nearly a year after the deadly virus began sweeping the world.
Trump's administration has led repeated attacks on Beijing, accusing officials of withholding vital information on the origins of the pandemic.
According to The Sun, US Secretary of State Mike Pompeo could declassify American intelligence concerning the lab as soon as Wednesday.
The parting shot in tensions between the US and China would be delivered just days before Joe Biden takes power.
The US Department of State has already published a stinging statement accusing the Chinese Communist Party of 'deceit and disinformation.'
The statement, released Friday, claims China knew of the outbreak long before it revealed the existence of the mysterious new illness to the world.
The US accuses Beijing of an obsession with 'secrecy' and of deliberately hampering researchers' and media efforts to trace the origin of Covid-19, which has now killed more than 2 million people worldwide.
The statement goes on to say that US officials have been unable to determine whether the outbreak "began through contact with infected animals or was the result of an accident at a laboratory in Wuhan."
The statement lays out a series of claims, blasting the lab's claim there was “zero infection” among its staff.
It alleges 'several' researchers inside the Wuhan lab became sick with symptoms consisted with Covid-19 or seasonal illness in autumn 2019.
It also alleges the lab could have military and biological weapons links.
The statement does not lay out evidence supporting any of the claims.
Beijing has continuously denied any suggestion the virus leaked from the lab.
A leading scientific theory throughout the pandemic suggests the virus may have originated in a Wuhan wet market, where it 'jumped' from animals to humans.
Scientists had for years warned governments that the consumption of exotic animals could trigger a pandemic.
Downing Street has repeatedly said China has questions to answer about the origins of the disease, but declined to back any one theory about how it started.
Asked if the UK shares the US assessment that Wuhan lab workers were sick in Autumn 2019, Dominic Raab told LBC: “I’m reticent about talking about anything which is sensitive material.”
Raab adds “we’re not clear yet” and there are different reports of how virus started.
Asked if he can’t rule out prospect it was leaked from lab, says: “We don’t have the evidence to corroborate that in any definitive way. What we want is to get the answers to those questions.”
He said China must provide access to investigators and there have been "teething issues" with getting the WHO review started. they should conduct review "without fear or favour and give the answers that people want".
Boris Johnson referenced the wet market transmission theory in comments at a summit last week.
The Prime Minister said: “Like the original plague which struck the Greeks I seem to remember in book one of the Iliad, it is a zoonotic disease.
"It originates from bats or pangolins, from the demented belief that if you grind up the scales of a pangolin you will somehow become more potent or whatever it is people believe.
"It originates from this collision between mankind and the natural world and we’ve got to stop it."
WHO researchers last week arrived in China to launch their long-delayed mission to investigate the pandemic's origins.
Asked on Sky News on Thursday if the team would investigate whether the virus was produced in a laboratory, WHO spokesman Tarik Jasarevic responded: "We will follow wherever science leads us.
"The majority of scientists believe there is a natural origin of the virus, we know that bats are a natural reservoir of other coronaviruses, we really want to go and see and get the data.
"You mentioned the market [Wuhan wet market] but it is possible there are cases of SARS-CoV-2 before the market and the market was just a spreading event.
"What is really important is to be open and to follow the leads from a scientific perspective."