The president attacked those who favored China, including the WHO, for which he previously announced a hold on funding

Donald Trump has fuelled a media theory that the coronavirus pandemic began when the pathogen accidentally escaped a Chinese laboratory, teasing that “more and more we’re hearing the story”.

The US president’s TV network of choice, Fox News, has reported that “multiple sources” in the American government believe initial transmission of the virus was bat-to-human in a virology lab in Wuhan. Due to weak safety protocols, an infected lab worker then went to a wet market where the virus spread.

When the Fox News reporter John Roberts put this to Trump at a press briefing on Wednesday, he replied: “Well, I don’t want to say that, John, but I will tell you more and more we’re hearing the story.”

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The president is notorious for recycling content from Fox News in his remarks or tweets, and it was unclear whether he was privy to any other information to back the claim. He added: “We’ll see. When you say ‘multiple sources’, now there’s a case where you can use the word ‘sources’. But we are doing a very thorough examination of this horrible situation that happened.”

Trump added that he did not want to disclose any discussions he had with the Chinese president, Xi Jinping, about the laboratory.

The Pentagon’s top general, Mark Milley, cast doubt on the lab theory earlier this week, saying that US intelligence has looked into the possibility but that the “weight of evidence” thus far pointed towards “natural” origins.

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Since the outbreak of the virus in Wuhan in December, more extreme conspiracy theories have suggested that it was engineered as a bioweapon. There is no evidence for this. The scientific journal the Lancet has stated the virus appears to have come from wildlife. An analysis by scientists at the Wuhan Institute of Virology suggests that the virus’s genome is 96% similar to a coronavirus found in bats.

But the story running prominently on Fox News begins by stating the virus began “not as a bioweapon”, alleging incompetence rather than a malicious attack. This idea has gained more traction, especially among anti-China hardliners in Washington.

On Tuesday the Washington Post reported that state department cables had warned two years ago of safety issues at a Wuhan lab studying bat coronaviruses. The Post said: “The cables have fueled discussions inside the US government about whether this or another Wuhan lab was the source of the virus – even though conclusive proof has yet to emerge.”

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China’s extreme censorship and lack of openness about the virus have done little to quell the speculation. But conversely, healthy scepticism is guaranteed because of Fox News’ widely panned coverage of the pandemic as well as Trump’s habit of searching for distractions and excuses to shift blame.

At Wednesday’s coronavirus taskforce briefing, he lambasted the Voice of America radio station for its China coverage – “what things they say are disgusting toward our country” – and the World Health Organization (WHO) for giving Beijing the benefit of the doubt.

“It took them a long time to realise what was going on, but I have a feeling they knew exactly what was going on,” he said without evidence, having previously announced a hold on WHO funding. “Tragically, other nations put their trust in the WHO and they didn’t do any formal [travel] ban.”

Meanwhile Trump, under pressure to restart the economy, struck an optimistic note for America’s fight against the virus on a cold day in the White House rose garden. “The battle continues but the data suggests that nationwide we have passed the peak on new cases,” he said, without giving details to support the claim. “Hopefully that will continue, and we will continue to make great progress.

“These encouraging developments have put us in a very strong position to finalise guidelines on states for reopening the country.”

The White House will release the guidelines on Thursday, he added, after he and Vice-President Mike Pence hold calls with governors. “We think that some states can actually open up before the deadline of May 1.”

Trump added: “We’ll be the comeback kids – all of us … Tomorrow’s going to be a very big day … We’ll have some openings that will exceed our expectations. And they’ll be safe, they’ll be strong, but we want to get our country back. We’re going to do it, and we’re gonna do it soon.”

Facebook Twitter Pinterest A healthcare workers puts on a sterile gown while helping test patients for coronavirus in Virginia. Photograph: Chip Somodevilla/Getty Images

The reopenings are bound to be phased geographically and require flexibility. Pence, who heads the coronavirus taskforce, said: “The American people will be encouraged to know as we stand here today, 24% of the counties of this country have no reported coronavirus cases. In fact, half of the states in America have less than 2,500 cases per state.”

But public health experts have warned that the US, which has the biggest caseload in the world, must boost testing and contact tracing before loosening restrictions. Trump said the US has surpassed 3.3m completed tests but failed to answer governors’ concerns over how the process can be stepped up.

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In an unexpected turn, he also threatened to force Congress into a formal recess so that he can make recess appointments of federal officials, including judges. He falsely accused Democrats of leaving key administration positions unstaffed and making it “very hard” to govern.

“We have a tremendous number of people that have to come into government and now more so than ever before because of the virus … If the House will not agree to that adjournment, I will exercise my constitutional authority to adjourn both chambers of Congress.”

Trump added: “The current practice of leaving town while conducting phony pro-forma sessions is a dereliction of duty that the American people cannot afford during this crisis.”

Michael Beschloss, an author and historian, tweeted: “No President in history has ever used the Constitutional power to adjourn Congress ... Wilson, Taft and FDR were all urged to adjourn Congress and all refused.”