China criticized this Friday that there is speculation again with the theory that the coronavirus pandemic could have originated after a leak from a Chinese laboratory and affirmed that it is a politically motivated lie. These remarks came after the World Health Organization (WHO) insisted in its strongest terms yet that further investigation is needed into whether a laboratory accident could be to blame for the spread of the virus.

Foreign Ministry spokesman Zhao Lijian also rejected accusations that China had not fully cooperated with investigators, saying he welcomed a science-based investigation but rejected any political manipulation. He also reiterated calls for an investigation into “highly suspect labs like Fort Detrick and the University of North Carolina” in the US, where China suggested, without evidence, that the US was developing the coronavirus as a bioweapon.

“The lab leak theory is totally a lie invented by anti-China forces for political purposes, which has nothing to do with science,” Zhao told a daily briefing. “We always support and participate in science-based global virus tracing, but we strongly oppose any form of political manipulation,” he said.

The WHO’s stance in a report released Thursday marks a sea change from the UN health agency’s initial stance on the origins of the pandemic. A change that comes after many critics have accused the body of too quickly dismissing or downplaying a theory that put Chinese authorities on the defensive.

Following a tightly controlled visit to China last year, the WHO concluded it was “extremely unlikely” that the coronavirus would spread to humans from a laboratory in the city of Wuhan. Many scientists suspect that the coronavirus jumped from bats to people, possibly through another animal.

However, in Thursday’s report, the WHO expert group said “key data” was still missing to explain how the pandemic started. The scientists said the group “would remain open to whatever scientific evidence becomes available in the future to allow for a comprehensive test of all reasonable hypotheses.”

Identifying the source of a disease in animals often takes years. Scientists took more than a decade to identify the bat species that were the natural reservoir for SARS, a relative of COVID-19. The WHO expert group also noted that since laboratory accidents in the past have triggered some outbreaks, the theory cannot be ruled out.