A new report in the Wall Street Journal has added fuel to a theory over where the coronavirus came from.
On Sunday, the newspaper cited a previously undisclosed U.S. intelligence report.
They say three researchers from China's Wuhan Institute of Virology got sick and sought hospital care in November 2019 - months before China disclosed the COVID-19 pandemic.
That report goes beyond a State Department fact sheet from January, which said that the symptoms of the researchers were consistent with "both COVID-19 and common seasonal illness."
Debate as to the origins of the virus began even before the health crisis became a global one.
The Trump White House asserted that it escaped from Wuhan's virus lab.
Beijing has consistently denied this.
In response to Sunday's article, China's foreign ministry called the news 'hype' from the U.S., and accused it of trying to divert attention.
It reiterated that a WHO-led team investigating the pandemic's origins said a lab leak was 'extremely unlikely' after a visit.
In March however, countries including the U.S., Canada and the UK expressed concern about the WHO's investigations.
A U.S. National Security Council spokeswoman had no comment on the Journal's report.
Though she said Washington was working with the WHO and other member states to support an expert-driven evaluation of the pandemic's origins "free from interference or politicization."