President Donald Trump has suggested he has seen evidence coronavirus originated in a Chinese laboratory.
Earlier the US national intelligence director’s office said it was still investigating how the virus began.
However, the office said it had determined Covid-19 “was not manmade or genetically modified”.
China has rejected the lab theory and criticized the US response to Covid-19.
Since emerging in China at the end of 2019, the new coronavirus has killed 230,000 people worldwide including 63,000 in the US.
The pandemic has seen at least 3.2 million people infected, a million of them Americans, since the virus spread from the city of Wuhan.
At the White House on April 30, President Trump was asked by a reporter: “Have you seen anything at this point that gives you a high degree of confidence that the Wuhan Institute of Virology was the origin of this virus?”
“Yes, I have. Yes, I have,” said President Trump, without specifying.
“And I think the World Health Organization [WHO] should be ashamed of themselves because they’re like the public relations agency for China.”
Asked later to clarify his comment, the president said: “I can’t tell you that. I’m not allowed to tell you that.”
President Trump also told reporters: “Whether they [China] made a mistake, or whether it started off as a mistake and then they made another one, or did somebody do something on purpose?
“I don’t understand how traffic, how people weren’t allowed into the rest of China, but they were allowed into the rest of the world. That’s a bad, that’s a hard question for them to answer.”
In a rare public statement, the Office of the Director of National Intelligence, which oversees US spy agencies, said on April 30 it concurs with the “wide scientific consensus” regarding Covid-19’s natural origins.
The statement said: “The [intelligence community] will continue to rigorously examine emerging information and intelligence to determine whether the outbreak began through contact with infected animals or if it was the result of an accident at a laboratory in Wuhan.”
It was the first clear response from American intelligence debunking conspiracy theories – both from the US and China – that the virus is a bio-weapon.
The Wuhan Institute of Virology, which was founded in the 1950s, houses China’s first Biosafety Level 4 laboratory.
Such labs handle the most dangerous pathogens for which there are few available vaccines or treatments, and one of the areas the Wuhan facility studies is coronaviruses from bats.
President Trump has recently been escalating his war of words with China over the pandemic after what officials within the president’s administration had described as a truce with Beijing.
On April 29, he suggested China wanted him to lose his re-election bid in November.
President Trump has formerly accused Chinese officials of covering up the virus early on and saying they could have stopped the disease from spreading.
He has similarly criticized the WHO and withdrawn US funding for the global body.
China’s foreign ministry, meanwhile, has accused the Trump administration of trying to distract from its own problems tackling the crisis.