FBI Director Christopher Wray said on Tuesday the agency has assessed that a leak from a laboratory in Wuhan, China, likely caused the Covid-19 pandemic.

“The FBI has for quite some time now assessed that the origins of the pandemic are most likely a potential lab incident in Wuhan,” Wray told Fox News.

His comments follow a Wall Street Journal report on Sunday that the US Energy Department has assessed with low confidence the pandemic resulted from an unintended lab leak in China.

Four other agencies, along with a national intelligence panel, still judge that the pandemic was likely the result of natural transmission, and two are undecided, the Journal reported.

White House national security spokesman John Kirby said on Monday the US government has not reached a definitive conclusion and consensus on the pandemic’s origins.

Wray said he couldn’t share many details of the agency’s assessment because they were classified.

He accused the Chinese government of “doing its best to try to thwart and obfuscate” efforts by the United States and others to learn more about the pandemic’s origins.

China says ‘lab leak’ claims hurt US credibility

Meanwhile, Beijing has accused Washington of harming its own credibility with the recent claims.

“The United States once again stirs up the laboratory leak theory, which will not discredit China, which will further lower its own credibility,” foreign ministry spokesperson Mao Ning told a regular briefing on Wednesday.

He reiterated a longstanding and unsubstantiated Chinese claim that the virus could have escaped from the US military research lab at Fort Detrick, Maryland.

“The US should respect science and facts, cooperate with the World Health Organisation as soon as possible, invite international experts to conduct traceability research in its country, and share research results with the international community,” she said.

The scientific community sees it as crucial to determine the origins of the pandemic in order to better fight or even prevent the next one.