The directive came as health officials and scientists have renewed calls for a more rigorous examination.

WASHINGTON — President Biden ordered U.S. intelligence agencies on Wednesday to investigate the origins of the coronavirus, indicating that his administration takes seriously the possibility that the deadly virus was accidentally leaked from a lab, in addition to the prevailing theory that it was transmitted by an animal to humans outside a lab.

In a statement, Mr. Biden made it clear that the C.I.A. and other intelligence agencies had not yet reached a consensus on how the virus, which prompted a pandemic and has killed almost 600,000 Americans, originated in China. He directed them to report back to him in 90 days.

“I have now asked the intelligence community to redouble their efforts to collect and analyze information that could bring us closer to a definitive conclusion,” the president said.

Mr. Biden’s statement, his most public and expansive yet on the question of how the virus spread to humans, came as top health officials renewed their appeals this week for a more rigorous inquiry. And it followed mounting criticism of a report from an international team of experts convened by the World Health Organization that largely dismissed the possibility that the virus had accidentally escaped from a Chinese laboratory called the Wuhan Institute of Virology.

Deep uncertainty remains about the origins of a virus that spread to every part of the globe over 17 months. The assessments of scientists are largely unchanged: Many believe that a so-called natural spillover from animal to human remains the most plausible explanation. While U.S. intelligence agencies have collected some new evidence, the additional information is not enough to allow them to draw definitive conclusions about long-simmering theories regarding the lab in the city of Wuhan, the center of the outbreak.

But the president’s carefully worded directive underscored a new surge in interest about the lab, which President Donald J. Trump and some of his top aides repeatedly blamed for the pandemic. Some scientists attributed the renewed focus on the lab to Mr. Trump’s departure from the White House — and being less identified with the theory — while others said it reflected the deep frustrations with the recent W.H.O. report that was co-written by Chinese scientists.

President Biden said in a statement on Wednesday that the intelligence community had “coalesced around two likely scenarios” but had not definitively answered the question.
Doug Mills/The New York Times

Avril D. Haines, the director of national intelligence, has been working with various intelligence agencies, bringing together officials with divergent views to discuss them, to review the shifting science and to push for additional intelligence collection.

Still, Mr. Biden’s order was an abrupt example of presidential intervention in the collection of raw data by those charged with collecting and analyzing intelligence on his behalf. Presidents are often hesitant to appear becoming overly involved in the preparation of the intelligence briefings they receive, though Mr. Biden has been active in asking for intelligence reports on issues including Russian aggressions and domestic terrorism.

The president had asked in March for an internal assessment of the virus’s origins, which was delivered to him two weeks ago in his Presidential Daily Brief of intelligence, according to a senior White House official and an administration official. That started a discussion, the officials said, about declassifying some of the findings and having intelligence officials issue a public statement.

The statement — which described the lack of consensus among intelligence agencies — was ready this week, but Mr. Biden felt it would not help clarify the issue for the public, according to the senior official. And on Tuesday, China took a hard line against cooperating with the W.H.O. on further inquiries, which prompted Mr. Biden to press for a more robust United States investigation, the official said.

It was unclear whether Mr. Biden was also moved to act by a public shift in opinion by some scientists or political pressure from Mr. Trump’s Republican allies on Capitol Hill, who have repeatedly accused the president and Democrats of refusing to take the lab origin theory seriously.

Seizing a lull on the Senate floor on Wednesday night, Senators Mike Braun of Indiana and Josh Hawley of Missouri, both Republicans, passed their bill to declassify intelligence related to any potential links between the Chinese lab and the origins of the pandemic through unanimous consent. It came after the Senate on Tuesday unanimously agreed to include two Republican provisions to a huge package of China legislation aimed at prohibiting sending American funding to the Wuhan Institute of Virology or to China-based “gain of function” research, in which scientists intentionally try to make a pathogen more powerful.

“For over a year, anyone asking questions about the Wuhan Institute of Virology has been branded as a conspiracy theorist,” Mr. Hawley said. “The world needs to know if this pandemic was the product of negligence at the Wuhan lab, but the C.C.P. has done everything it can to block a credible investigation.”

In the past several days, the White House had played down the need for an investigation led by the United States and insisted that the W.H.O. was the proper place for an international inquiry. Mr. Biden’s statement on Wednesday was an abrupt shift.

Lam Yik Fei for The New York Times

The scientific and political debate about how the virus became a global threat to humans has been simmering since the beginning of the pandemic. For much of that time, scientists around the world have concluded that it most likely emerged from an infected animal.

There was clear evidence for the coronavirus having emerged naturally through the recombination of genetic material from different bat coronaviruses, said Dr. Robert Garry, a virologist at the Tulane University School of Medicine. The data so far bears the hallmarks of natural recombination, he said, and no signs of human intervention.

“The pieces are out there,” Dr. Garry said. “These viruses mix bits and pieces all the time.”

But others have long suspected that the global health crisis was man-made, pointing to the Chinese lab as the likely source of the pathogen. Mr. Trump repeatedly accused the Chinese of covering up their complicity. Peter Navarro, Mr. Trump’s trade adviser, suggested that it had been created in a Chinese bioweapons lab.

Days before he left office, Secretary of State Mike Pompeo released a fact sheet about the Wuhan Institute of Virology, outlining evidence that the virus might have emerged accidentally from the facility. Among other data points Mr. Pompeo released was that the government had “reason to believe that several researchers inside the W.I.V. became sick in autumn 2019, before the first identified case of the outbreak, with symptoms consistent with both Covid-19 and common seasonal illnesses.”

The Wall Street Journal reported on Sunday that the information about the sick researchers released by Mr. Pompeo had been contained in intelligence documents prepared at the end of the Trump administration.

At least two intelligence documents produced in recent months discuss the sick workers, according to an American official. One is narrowly focused on information about the three people, and a broader document put the intelligence in the context of what is known about the origins of the coronavirus.

Erin Schaff/The New York Times

The intelligence on the three workers came from outside the United States intelligence agencies’ own collection, which means its veracity is more difficult to authenticate. The source of the information was unclear, but several American officials said they believed the report that the three researchers got sick.

American intelligence officials do not know whether the lab workers contracted Covid-19 or some other disease, like a bad flu. If they did have the coronavirus, the intelligence may suggest that they could have become sick from the lab, but it also could simply mean that the virus was circulating in Wuhan earlier than the Chinese government has acknowledged.

Also toward the end of Mr. Trump’s term, State Department officials began examining the origins of the virus and concluded that it was highly unlikely to have appeared naturally and thus was likely the product of laboratory work.

CNN first reported the effort and suggested that the group’s efforts had been shut down by the Biden administration, prompting scathing Republican criticism. A State Department spokesman, Ned Price, denied that, saying that the team’s findings were briefed to senior officials in the department’s arms control bureau in February and March.

“With the report delivered, the work was ended,” Mr. Price said.

Mr. Trump issued a statement on Tuesday boasting of his early insistence that the Wuhan lab was the source of the virus. “To me, it was obvious from the beginning,” he said. “But I was badly criticized, as usual.”

Despite the absence of new evidence, a number of scientists have lately begun speaking out about the need to remain open to the possibility that the virus had accidentally emerged from a lab, perhaps after it was collected in nature, a lab origin distinct from a creation by scientists.

“It is most likely that this is a virus that arose naturally, but we cannot exclude the possibility of some kind of a lab accident,” Dr. Francis Collins, the director of the National Institutes of Health, told senators on Wednesday.

Some scientists attributed the shift in part to the fact that the more extreme proponents of a lab leak hypothesis, like Mr. Navarro, had drowned out the more measured discussions of how lab workers could have accidentally carried the virus outside.

Scientists had been reluctant to discuss the lab leak hypothesis last year because they had been on guard against disinformation, said Marc Lipsitch, a Harvard epidemiologist.

“Nobody wants to succumb to conspiracy theories,” he said.

But the March report by the group of W.H.O.-chosen experts in collaboration with Chinese scientists, dismissing the possibility of a lab leak as “extremely unlikely,” compelled some scientists to speak out.

“When I read that, I was very frustrated,” said Akiko Iwasaki, an immunologist at Yale University. Along with Professor Lipsitch, she signed a letter published in the journal Science this month saying that there was not enough evidence to decide whether a natural origin or an accidental laboratory leak caused the coronavirus pandemic.

“I think it’s really an unanswered question that really needs more rigorous investigation,” Dr. Iwasaki added.

Anindito Mukherjee/Getty Images

From the earliest weeks of the outbreak, the Chinese government has worked to delay, deflect or block independent investigation of the virus’s origins.

Chinese officials said in early 2020 that the outbreak began at a Wuhan market, and they blamed illegal wildlife sales there. They did so despite having evidence that undermined that theory: Early data showed that four of the first five coronavirus patients had no clear links to the market. The government resisted accepting an international scientific mission.

The World Health Organization gave early cover to China’s dissembling, incorrectly praising Chinese disease surveillance with spotting an outbreak that it had actually missed. The health organization publicly announced that China had agreed to share biological samples — but never followed up to say that the government had failed to deliver on that promise.

Hector Retamal/Agence France-Presse — Getty Images

China has also pushed conspiracy theories, including that the disease was spread by the American military, and argued that any origin investigation should start in Europe, not in China. Chinese officials and state media have also frequently taken a defensive stance.

On Wednesday, Zhao Lijian, a Foreign Ministry spokesman, sidestepped a question about whether the W.H.O. would be permitted to do further investigation in China, saying that an “authoritative study report” with “many significant conclusions” had already been issued.

Instead, Mr. Zhao sought to deflect attention from China, pointing to what he called the reports of Covid-19 being detected as early as 2019 in other parts of the world. He also referred again to the baseless theory that the virus came from a United States Army lab.

“China takes the origin-tracing work seriously with a responsible attitude, and has made positive contributions that are widely recognized,” Mr. Zhao said. “If the U.S. side truly demands a completely transparent investigation, it should follow China’s lead to invite the W.H.O. experts to the U.S.”

Even as the debate about the virus’s origins has resurfaced in recent weeks, there has been little public discussion of the issue in China. On Wednesday, many on Chinese social media were more preoccupied with discussing the death of Yuan Longping, a prominent plant scientist, and a deadly ultramarathon in the northwestern Chinese region of Gansu.

Reporting was contributed by James Gorman, Noah Weiland, Catie Edmondson, Amy Qin, Matt Apuzzo, Selam Gebrekidan and Michael Crowley.