"I can't tell you that. I'm not allowed to tell you that," Trump said at a White House event when asked what evidence he has seen to make him believe that the virus emerged from the Wuhan Institute of Virology in China.
That lab is in the region that saw the first big outbreak of what is now a world-wide pandemic that has infected more than 3.2 million people.
Trump's comments went much further than a statement from the top US intelligence agency on Thursday, which said, for the first time, that it, "Concurs with the wide scientific consensus that the COVID-19 virus was not manmade or genetically modified."
But the Office of Director of National Intelligence added that the American 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."
Before Trump spoke Thursday, The New York Times reported that senior Trump administration officials "have pushed American spy agencies to hunt for evidence to support an unsubstantiated theory" that the Wuhan laboratory was the point of oring for the outbreak.
"The effort comes as President Trump escalates a public campaign to blame China for the pandemic," The Times noted.
Trump initially was asked by a reporter at the White House on Thursday about the origins of the virus, and answered, "You have heard all different things. Three or four different concepts as to how it came out."
"We should have the answer to that in the not-so-distant future and that will determine a lot how I feel about China," the president said.
But he later was asked by a reporter if he had "seen anything that gives you a high degree of confidence, at this point, that the Wuhan Institute of Virology was the source of this virus?"
Trump replied, "Yes, I have," and then repeated that assertion.
"I think that the World Health Organization should be ashamed of themselves, because they're like the public relations for China," Trump added, implying that the international health agency was covering up for China.
"This country," Trump said, referring to the United States, "pays them [WHO] almost $500 million a year, and China pays them $38 million a year."
"They [WHO] shouldn't be making excuses when people make horrible mistakes, especially mistakes that are causing hundreds of thousands of people around the world to die."
Asked if he was suggesting that the coronavirus was not naturally occurring, Trump said, "No."
"We're going to see where it is, where it comes from, theory from lab, the bats, the type of bat, couldn't have been here or there, a lot of theories," Trump said. "We have people looking at it strongly, scientific people, intel people."
But when pressed on what gave him a high degree of confidence to believe that the virus came out of the Wuhan lab, Trump demurred, saying, "I can't tell you that. I'm not allowed to tell you that."
Trump announced two weeks ago that the United States would halt funding to WHO.
He had earlier threatened to withhold funds by claiming that WHO pushed back on his travel ban from China early in the Covid-19 outbreak. Trump later claimed that WHO "pushed China's misinformation about the virus, saying it wasn't communicable and there was no need for travel bans."
"The WHO willingly took China's assurances at face value, and they willingly took it at face value and defended the actions of the Chinese government even while praising China for its so-called transparency," he said.
World health officials have said the virus likely emerged from a seafood market in Wuhan.
International officials said the virus likely originated in bats and then jumped to an "intermediate host" before infecting humans.
SARS, an earlier coronavirus that emerged in November 2002 and killed nearly 800 people across the world over nine months, also was believed to have originated in bats before spreading to civet cats and, later, to humans.
There have been about 228,000 deaths worldwide, at least, from Covid-19, since the outbreak began.
In the United States, currently the epicenter of the pandemic, there have been more than 1 million people infected, with about 61,000 deaths related to the coronavirus.