A team of World Health Organization scientists said Tuesday in China that the coronavirus likely first spread to humans via an intermediate animal host and was “extremely unlikely” to be the result of a laboratory accident.

The results, presented by the team in Wuhan, China, after 12 days of fieldwork, were the first step in a most likely painstaking process to trace the origins of the global pandemic. This question is crucial to prevent recurrence.

“All of the work that has been done on the virus trying to identify its origin continues to suggest a natural reservoir,” said Dr. Peter K. Ben Embarek, a food safety scientist at WHO who leads the team of experts, at a press conference in Wuhan, the city where the coronavirus was first discovered in late 2019.

The WHO experts largely focused their comments on the scientific aspects of their mission. However, the investigation has been overshadowed by politics in many ways. The Chinese government has further warned that the virus may have come from overseas, an idea many scientists are rejecting. Chinese officials used Tuesday’s press conference to further advance this theory, arguing that the search for the virus’ origin should focus on locations outside of China.

The visit was also an opportunity for WHO to dispel criticism that it is too respectful of China.

For months, experts and politicians have condemned the WHO for allowing the Chinese government to control the investigation into the cause of the pandemic. Chinese officials, careful not to point out missteps during the outbreak, repeatedly delayed visits by WHO experts and tried to narrow the scope of their mission. The Chinese government gave in to mounting global pressure and finally let the 14-person team go to Wuhan last month.

Updated

Apr. 9, 2021, 6:44 p.m. ET

The WHO used the research to project an image of transparency and independence. During their stay in Wuhan, the team of scientists used social media to record their visits to laboratories, disease control centers and live animal markets. WHO officials have vowed to ask tough questions and press for access to data and research, but it remains unclear how soon the Chinese government will be.

“If the team can’t come up with a substance, there’s a risk that people will say this is all just a show,” said Daniel R. Lucey, an infectious disease specialist at Georgetown University.

The investigation takes place in a charged political environment. Chinese Ambassador to the United States, Cui Tiankai, recently suggested that the United States allow WHO to send investigators there as part of its investigation.

Officials in the United States and other Western countries have at times expressed doubts about the independence of the WHO investigation, fearing that China may try to influence the results.

Now it will be up to the team of scientists to conduct a difficult study that many say could take months or even years.

While China ultimately cooperated with the visit, the government still has a firm grip on research related to the virus in China and could try to prevent any embarrassing information from being published.

“One visit is not enough for a thorough investigation,” said Yanzhong Huang, senior fellow on global health with the Council on Foreign Relations. “They do all the work within the parameters set by the Chinese government.”

The WHO team commended the Chinese scientists involved in the mission and said the government had worked in good faith to provide access to key locations such as the Huanan Seafood Wholesale Market, where some of the earliest cases were discovered . Scientists were also allowed to visit the Wuhan Institute of Virology, which is home to a state-of-the-art laboratory that has been at the center of several unfounded theories about the virus.

Albee Zhang contributed to the research.