Geneva, Switzerland - The World Health Organization (WHO) has asked Washington for the underlying information behind the assessment by some US intelligence agencies that the coronavirus pandemic was most likely started by an accidental lab leak in China.

Requests had been made to the US diplomatic mission in Geneva, but so far no reports had been received, WHO expert Maria Van Kerkhove said on Friday.

Christopher Wray, the head of the Federal Bureau of Investigation (FBI), told the Fox News channel on Tuesday that the agency believes "the origins of the pandemic are most likely a potential lab incident in Wuhan." The worldwide pandemic started in the Chinese city.

The FBI added that it was "a possible leak from a Chinese government-controlled laboratory" that caused the pandemic.

According to a report in the Wall Street Journal and other US media, the US Department of Energy is now also assuming a possible lab leak, albeit with a "low" degree of certainty.

There is no consensus in Washington's intelligence community on the precise emergence of Covid-19. Other agencies point to the possibility of the virus naturally jumping from animals to human.

Scientists have been searching for the origin of the pandemic for three years. A WHO delegation was in China at the beginning of 2021, but Beijing refused further trips by international experts. The WHO has recommended several investigations in China and elsewhere, but they have not happened so far.

In Wuhan, where Covid-19 illnesses first appeared in late 2019, research on coronaviruses is carried out in government-controlled lab. China categorically denies that the virus could have escaped from it.

The origin must be found to prevent future pandemics if possible, WHO chief Tedros Adhanom Ghebreyesus said.

He said the "WHO continues to call for China to be transparent in sharing data, and to conduct the necessary investigations and share the results."

He said he had written and spoken with "high-level Chinese leaders on multiple occasions, as recently as just a few weeks ago."

"Until then, all hypotheses on the origins of the virus remain on the table."