US President Joe Biden said on Wednesday he is calling on the intelligence community to submit a report within three months on the origins of Covid-19 amid a resurgent debate over how the virus appeared.
Mr Biden said the report should look into "whether it emerged from human contact with an infected animal or from a laboratory accident", and present questions that may require confirmation, including some for China.
"I have now asked the intelligence community to redouble their efforts to collect and analyse information that could bring us closer to a definitive conclusion and to report back to me in 90 days," he said.
The move comes during a growing controversy on how to handle an investigation into the origins of the virus, which has killed more than 3.5 million people globally.
“We need to get to the bottom of this," deputy White House press secretary Karine Jean-Pierre said.
"As we all know, we’ve lost almost 600,000 Americans to Covid-19 and we have to get a better sense of the origins of Covid-19 and also, how do we prevent the next pandemic?”
The first virus cluster was reported to the World Health Organisation in late 2019 in Wuhan, China, home to the Wuhan Institute of Virology, fuelling theories that Covid-19 might have escaped from the lab.
Chinese Foreign Ministry spokesman Zhao Lijian on Wednesday said the US was “spreading conspiracy theories and disinformation, such as a laboratory leak".
“Some people in the United States claim they want the truth but their real intention is political manipulation,” Mr Zhao said.
Members of the former president Donald Trump's administration favoured the laboratory leak theory, including former Centres for Disease Control and Prevention chief Dr Robert Redfield.
Many scientists, including WHO members, say the theory is unlikely.
The UN agency co-ordinated an investigation by independent scientists who visited Wuhan, China, and their report concluded that the virus most probably jumped to humans from bats.
Meanwhile, there are concerns that investigations into Covid's beginnings could fuel anti-Asian sentiment, which has increased in the US in recent months.
Mr Biden has signed an anti-hate crimes bill in response to several attacks on Asian Americans.
Scientists assert that finding the virus's origin would help the global community to prevent or prepare for the next pandemic, by figuring out how to protect against diseased animals or how to best improve medical lab security.
Top US infectious diseases expert Dr Anthony Fauci said he was "not convinced" that Covid-19 had developed naturally.
"I think we should continue to investigate what went on in China until we continue to find out to the best of our ability what happened," Dr Fauci said.
"Certainly, the people who investigated it say it likely was the emergence from an animal reservoir that then infected individuals, but it could have been something else and we need to find that out.
"So, you know, that's the reason why I said I'm perfectly in favour of any investigation that looks into the origin of the virus."