The administration of former U.S. President Donald Trump advanced a theory that the Wuhan Institute of Virology might be the birth of the virus, but China has rejected the allegation, further fueling tensions between the world's two major powers.

Vladimir Dedkov, deputy director for scientific work of the St. Petersburg Research Institute of Epidemiology and Microbiology, on Wednesday visited the laboratory in Wuhan, the original epicenter of the outbreak, along with nine other WHO experts.

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"Of course, it was important for our mission to visit this facility, talk to our colleagues and see how everything is organized there," the Russian expert was quoted as saying by his country's Sputnik news agency.

"The laboratory is perfectly equipped," he said. "It is hard for me to imagine that something could have leaked from there."

Dedkov also referred to a Wuhan market, at which many people were confirmed to have contracted the new virus in the early days of the epidemic in late 2019. The WHO team carried out a one-hour investigation into the place on Sunday.

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"I'm not very familiar with the sanitary rules of China, but looking at this, extrapolating to our legislation, of course, the market is very far from perfect," he said. "There is no evidence that the virus originated there" but "hypothetically, there are all conditions for the spread of the virus there."

The market, where wild animals such as bats and snakes had been sold alongside seafood, has been closed since January 2020. It has been sanitized thoroughly by Chinese authorities.

The WHO has been trying to clarify the process of how bats, believed to be the main natural host of the virus, passed it to other animals, sources close to the matter said.

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After quarantining for two weeks, the WHO experts began a full-fledged probe in late January. They are likely to complete the investigation in Wuhan by the Feb. 11 start of the weeklong Lunar New Year holidays, the sources added.

In July, the WHO sent a small group to China for a preliminary probe, but they did not visit the market or the laboratory.