During a press conference at the White House, Trump said he had seen evidence that a laboratory in China had been the source of the outbreak, although he refused to elaborate.

“Yes, I have,” Trump said, referring to evidence pointing to the Wuhan Institute of Virology – where the coronavirus has been studied.

When asked about reports that he could decide to default on US debt obligations to China, Trump said he could “do it differently” and act in “probably a little bit more of a forthright manner”. “I could do the same thing but even for more money, just putting on tariffs,” he said.

But People’s Daily, the mouthpiece of the Communist Party, denounced Trump’s call for compensation from China as “deception”.

“This kind of ridiculous behaviour will not threaten China,” a commentary published by the paper on Friday said, without naming Trump.

“Some US politicians are calling for punishment because they have nowhere to hide their responsibility,” it said. “It would be naive to believe that China will fall for this.”

The previous day, People’s Daily had listed 10 questions for the US to answer. For example, it said the US government had to explain to the world about a bird influenza virus modification experiment it approved in 2018, citing a report from the journal Science.

The paper called the experiment – aimed at transforming the H5N1 virus to be more capable of infecting mammals – “extremely dangerous”, and demanded Washington disclose its progress and explain why it had resumed after four years of suspensions.

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The post, published on a social media account of People’s Daily, stopped short of mentioning the rationale for such studies, which advocates say can help public health experts better understand how viruses might spread and plan for pandemics, according to the report by Science, published in February 2019.

People’s Daily also said Washington should explain a simulation exercise it conducted last year under the scenario of a pandemic flu outbreak that originated in China and was highly contagious, citing a report by The New York Times.

Other questions it asked were related to Washington’s slow response to the pandemic before March.

US politicians have suggested that the coronavirus could have originated from the Chinese lab. Beijing has denied the allegation, and at one point spread a conspiracy theory that the virus had been brought to the central Chinese city of Wuhan by the US army.

Scientists believe the virus jumped from animals to humans, after cases were initially reported in late December at a Wuhan market selling exotic animals. Many scientists have said there is no evidence to conclude that the virus came from the lab.

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In an unusual move, the US’ Office of the Director of National Intelligence on Friday said that it was trying to determine whether it could have leaked from the Wuhan lab.

“The intelligence community also concurs with the wide scientific consensus that [the virus] was not man-made or genetically modified,” the office said in a statement.

But it 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.”

In Geneva, a spokesman for the World Health Organisation (WHO) said several investigations into the source of the virus were ongoing, but the global agency was “not currently involved in the studies in China”.

“WHO would be keen to work with international partners and, at the invitation of the Chinese government, to participate in investigation around the animal origins,” the spokesman told Agence France-Presse.

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When asked if he was concerned about the tensions between the United States and China harming international cooperation, Guterres said: “These are two absolutely vital countries. The contribution of China and the United States both to fight Covid-19 [and] to all other aspects in the development of international relations is, in my opinion, absolutely essential and I hope that it will become possible in the future.”

Shi Yinhong, a US specialist with Renmin University in Beijing, said it was more likely that Trump would take measures against China as November’s presidential election – in which he will try to win a second term – drew closer.

“The origin of the virus is a very significant political question, though I personally think it’s technically impossible to prove anything,” he said.

“But as the election gets tougher for Trump, he might make moves against China even before the pandemic is brought under control in the US.”

Victor Gao, a vice-president of the Centre for China and Globalisation, a Beijing think tank, said it would be extremely hostile for the US to default on US Treasury bonds held by China, the largest holder of the bonds.

“China thinks holding a lot of US Treasury bonds is a contribution to financial stability in the United States, as well as a major contribution to overall China-US relations,” he said.

“If the US really wants to do the extreme thing of cancelling [its debt], this will be tantamount to a declaration of war.”

Gao added that the phase one trade deal reached by the two countries could be “nullified” if Washington imposed extra tariffs on Chinese goods in response to the consequences of the pandemic.

Additional reporting by Cissy Zhou