Donald Trump claims he has seen evidence the novel coronavirus originated in a Wuhan laboratory – but has declined to give specifics.
Mr Trump said he feels confident the virus came from the Wuhan Institute of Virology, adding that US authorities were “looking at it very, very strongly”.
“We’re going to see where it is – we’re going to see where it comes from,” he said. “There’s a lot of theories.”
“China might even tell us,” he added.
Asked by a reporter whether he had seen “anything that gives you a high degree of confidence” the institute was the origin of the virus, he responded: “Yes I have.”
And asked a few minutes later what gave him such confidence, he said: “I can’t tell you that. I’m not allowed to tell you that.”
The Wuhan Institute of Virology has dismissed the allegations and other US officials have downplayed their likelihood.
Chinese Foreign Ministry spokesman Geng Shuang said: “I would like to point out again that the origin of the virus is a complex scientific issue, and it should be studied by scientists and professionals.”
He also said the US should spend their time on “better controlling the pandemic at home”.
It is widely believed the virus originated in a seafood market in a Chinese city, having jumped from animals to humans.
Last month, Sky News revealed the UK was among the countries investigating the origin of the coronavirus pandemic, including a possibility it could be linked to a Chinese laboratory conducting research into diseases in bats.
A US official was quoted by NBC News as saying it was “a possibility, though not the most likely possibility”.
It is thought to be considered highly likely the novel coronavirus did occur naturally and is not man-made.
Mr Trump declined to say whether he holds Chinese President Xi Jinping responsible for what he feels is misinformation.
But he did criticise China for failing to contain the virus, saying: “This is something that could have been contained at the original location and it could have been contained relatively easily.”
He later added: “One of two things happened. They either couldn’t do it from a competence standpoint or they let it spread.
“I would say probably it got out of control.”
Tensions between Beijing and Washington have heightened in recent weeks, with China suggesting the US military might have brought the coronavirus to China.
On Wednesday, Mr Trump said he was looking at imposing consequences for China over the virus.
More than 61,000 people in the US have died after contracting coronavirus, according to Johns Hopkins University.