Wuhan, China - Three researchers at a virology lab in China's Wuhan became ill enough to seek hospital care in November 2019, the Wall Street Journal reported on Sunday, citing a US intelligence report.

The previously undisclosed report could fuel calls for a deeper probe into the theory that the coronavirus escaped from the Chinese lab, though a World Health Organization (WHO) group of experts said earlier this year it was "extremely unlikely."

The WSJ report came on the eve of a WHO meeting expected to address the next phase of investigation into the pandemic's origins.

A US State Department fact sheet issued during Donald Trump's final days in office in January said several researchers at the Wuhan Institute of Virology (WIV) became ill in autumn 2019 with symptoms consistent with both Covid-19 and common seasonal illnesses.

The intelligence document goes further in disclosing the number of researchers, the timing of their illness and their hospital visits.

One official cited by the WSJ said the intelligence was in need of further investigation and corroboration, while another said the information was "very precise" but did not explain why the researchers became ill.

Trump's administration pushed the theory that the virus originated in a Wuhan lab, while the administration of President Joe Biden has called for more evidence before concluding an origin of the virus.

The WHO researchers did not reach a definitive conclusion on the virus's origins in February after they visited Wuhan, where the first coronavirus outbreak was detected at the Huanan market in late 2019.

China has consistently denied the lab-leak theory.