'Not convinced' COVID-19 developed naturally: Dr Fauci

America's top expert on infectious diseases, Dr Anthony Fauci said he is "not convinced" the novel coronavirus developed naturally and has called for an open investigation into the origins of COVID-19 virus.

When Dr Fauci was asked at an event whether he was still confident that the coronavirus developed naturally he said: "I am not convinced about that. I think we should continue to investigate what went on in China until we continue to find out to the best of our ability what happened."

"Certainly, the people who investigated it say it likely was the emergence from an animal reservoir that then infected individuals, but it could have been something else, and we need to find that out. So, you know, that's the reason why I said I'm perfectly in favour of any investigation that looks into the origin of the virus," Dr Fauci was quoted by Fox News.

The Biden administration's top medical adviser made these remarks during 'United Facts of America: A Festival of Fact-Checking' event.

When he was asked categorically about whether the COVID-19 virus could not have occurred by serial passage in a laboratory, the director of the National Institute of Allergies and Infectious Diseases said that he is fully in favour of any further investigation of what went on in China.

However, he did not explicitly rule out such a possibility.

He repeated that the NIH and NIAID categorically have not funded gain of function research to be conducted in the Wuhan Institute of Virology.

Last year Dr Fauci had largely dismissed the theory that the deadly COVID-19 virus, due to which over 165 million people have been infected worldwide and over 3.5 million peope died so far, was genetically engineered and had leaked from a lab in Wuhan, China.

Fox News noted that the Donald Trump administration officials and Republicans have long argued there is a high chance COVID-19 was the result of a lab leak in China.

The World Health Organization had last week declared the lab leak theory "extremely unlikely", but even Dr Tedros Adhanom Ghebreyesus, WHO chief, has said the research team's assessment on whether the virus entered the human population following a laboratory incident was not "extensive enough" and requires further investigation.

The White House has not yet said whether it's seen evidence to disprove the lab leak theory, but has joined calls for an independent investigation.