A top Wuhan laboratory official has denied any role in spreading the new coronavirus, in the highest-level response from a facility at the center of months of speculation about how the previously unknown animal disease made the leap to humans.

Yuan Zhiming, the Wuhan Institute of Virology’s Communist Party chief, hit back at those promoting theories that the virus had escaped from the facility and caused the outbreak in the central Chinese city. “There is absolutely no way that the virus originated from our institute,” Yuan said in an interview Saturday with the state-run China Global Television Network.

Yuan rejected theories that the yet-to-be identified “Patient Zero” for Covid-19 had contact with the institute, saying none of its employees, retirees or student researchers were known to be infected. He said U.S. Senator Tom Cotton, an Arkansas Republican, and Washington Post journalists were among those “deliberately leading people” to mistrust the facility and its “P4” top-level-security pathogen lab.

U.S. President Donald Trump again fanned speculation about the origins of the virus at a Saturday news conference, in which he said China should face consequences if it was “knowingly responsible” for the outbreak. The U.S. president has at times referred to the disease as a “Chinese virus,” a term he said he embraced after a Chinese foreign ministry spokesman tweeted an unsubstantiated theory about U.S. Army athletes introducing the pathogen to Wuhan.

“What we know is that the ground zero for this virus was within a few miles of that lab,” Peter Navarro, a Trump trade adviser, said Sunday on Fox News. “If you simply do an Occam’s razor approach that the simplest explanation is probably the most likely, I think it’s incumbent on China to prove that it wasn’t that lab.”

The U.S.-China blame game has helped fuel scrutiny of the Wuhan lab, which was studying bat-borne coronaviruses like the one that causes Covid-19. U.S. diplomats sent back warnings about safety procedures in the lab after visits two years ago, the Washington Post reported in an April 14 commentary, citing diplomatic cables.

“They don’t have any evidence on this, what they rely on is only their guess,” Yuan told CGTN on Saturday. “I hope such a conspiracy theory will not affect cooperation among scientists around the world.”

Some countries including Australia have urged an independent review of how the pandemic came to infect more than 2.4 million people and kill more than 166,000. “The issues around the coronavirus are issues for independent review and I think that is important that we do that, in fact Australia will absolutely insist,” Foreign Minister Marise Payne told ABC Australia’s “Insiders” program Sunday.

While many Republicans have emphasized the Chinese origins of a virus that has killed more than 40,000 Americans, Cotton has been among the most vocal urging an investigation into the lab’s role. On Friday, he told Fox News that “circumstantial evidence” was “stacking up pretty quickly that this virus may have originated in those labs in Wuhan.”

Although the first known cluster centered on a wet market in Wuhan, the ultimate origins of the virus remain a mystery and Chinese officials have raised the possibility that the virus didn’t begin in the country at all. Meanwhile, General Mark Milley, the chairman of the U.S. Joint Chiefs of Staff, has endorsed studies that have shown the virus evolved naturally, as opposed to being genetically engineered.

Yuan’s interview represents the highest-level response from the lab since speculation about its role began in January. Shi Zhengli — a researcher at the institute known as “Bat Woman” for her expeditions in bat caves — said in a February social media post that she would “swear on my life” that the virus had nothing to do with the lab.

On Feb. 19, the Wuhan Institute of Virology issued a letter to staff, saying it received its first sample of the virus from Wuhan Jinyintan Hospital on Dec. 30, a day before Chinese authorities first disclosed the outbreak to the world. Researchers finished gene-sequencing in 72 hours and submitted its findings to the national virus database by Jan. 9, the institute said, adding “we have a clear conscience looking back on what we’ve gone through.”

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