Donald Trump claims he has seen evidence the novel coronavirus originated in a Wuhan laboratory – but has declined to give specifics.
Speaking at a White House news conference, the US president said China either could not stop spread of the virus, or let it spread.
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.”
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The Wuhan Institute of Virology has dismissed the allegations and other US officials have downplayed their likelihood.
It is widely believed the virus originated in a wet market in a Chinese city, having jumped from animals to humans.
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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.