The U.S. intelligence community remains divided in its report on the origins of COVID-19 because their work was "intelligence-based instead of science-based," Chinese virologists said after the report was released on Friday.

A Chinese virologist told CGTN on condition of anonymity that the report shows the U.S. intelligence community generally tends to believe the novel coronavirus came from nature, but they lack evidence and confidence in the conclusion. A small number of people still think it might have something to do with a "lab leak."

The divided opinions inside the U.S. intelligence community rooted in their intelligence-based research method, the expert said.

"But the report ruled out the possibility that the virus was man-made or genetically engineered. It also acknowledged that the Chinese government did not have foreknowledge of the virus before the initial outbreak of COVID-19," the expert said.

Another Chinese virologist close to the World Health Organization (WHO) - China joint study on origins tracing wrote in a statement to CGTN that the U.S. intelligence community continues to include the extremely unlikely laboratory incident as the potential origin for SARS-CoV-2.

The report "unfairly criticized China's cooperation with the WHO, even though no other countries have invited the WHO to conduct origins tracing research twice since the pandemic began," the expert added.

"Politicizing the issue is the most negative factor in delaying global efforts to trace the origins of the virus," the expert stressed.

When asked whether the intelligence community should be involved in COVID-19 origins tracing, Marion Koopmans, a Dutch virologist and member of the WHO-China joint team who came to Wuhan in March, said in a written interview with CGTN that "I do not think that is up to me. The intelligence community defines its own agenda."

"However, I do think that the discussion about origins has a political angle that makes it more difficult to work together as scientists," she wrote.

"It is part of the reality, and understandable given the impact of this pandemic and the global interest in finding the origins. But mixing political and scientific discussions is not a good combination," she added.

Koopmans and 10 other international scientists on the WHO's SARS-CoV-2 origins tracing team to China published an article in Nature on Wednesday. They warned that "the window of opportunity for conducting the inquiry is closing fast."

Koopmans further elaborated on that in the interview with CGTN.

"We recommended specific studies, some of which are time sensitive. For instance, going back to test blood donations collected in the second half of 2019. We discussed this in Wuhan and were told donations would be kept, although normally they will be destroyed after two years. So in Wuhan this will still be possible. But we recommend studies in all places where there was evidence for early circulation, inside and outside China," she said.

In the Nature article, the international scientists listed six priorities for follow-up origins-tracing studies, highlighting critical trace-back of people and animals in regions inside and outside China that have the earliest evidence for circulation of the virus, and targeted surveys of possible reservoir or intermediate animal hosts of the virus.

But it did not include the "lab leak" theory as a priority. They said in the article that no new evidence supporting the "lab leak" hypothesis has been reported to the WHO so far.

Koopmans told CGTN that they still stand by their conclusions in the WHO-China joint report, that a zoonotic spillover is the most likely origin of the virus.

"We feel that all cards are still on the table as long as we really do not know what happened. SARS-CoV-2 is a close relative of bat viruses, but what the steps in between have been we do not know. For instance, if the serological study would find evidence for pockets of cases earlier, that is where we would recommend detailed epidemiological investigation, including asking about lab work. We still stand by our conclusions in the report that we consider a zoonotic spillover the most likely pathway," she said.

In a response to the U.S. intelligence community's report, Zeng Yixin, deputy minister of the National Health Commission, said on Sunday that China supports the expansion of coronavirus origins tracing to comprise probes into multiple countries, including the U.S. He also said that COVID-19 origins tracing is a "scientific job."

"Therefore, the Chinese government has always stated that the job should be conducted in a scientific way, and China opposes politicizing it," he stressed.

That's been echoed in the Nature article that "understanding the origins of a devastating pandemic is a global priority, grounded in science." 

(CGTN's Cao Qingqing contributed to the report.)