US Secretary of State Mike Pompeo on Friday called on China to grant the United States access to the Wuhan laboratory that has emerged as a flashpoint between the two nations in a clash over the origin and handling of the coronavirus.

“We are still asking the Chinese Communist Party to allow experts to get into that virology lab so that we can determine precisely where this virus began,” said Pompeo on Fox News.

Pompeo’s comment escalated conjecture surrounding the lab as US President Donald Trump amplified doubts around the extent of the Covid-19 spread in China by announcing in a Twitter post that the country “has just announced a doubling in the number of their deaths from the Invisible Enemy. It is far higher than that and far higher than the US, not even close!”

The tweet was not accurate as China only announced a revised increase in deaths out of Wuhan by 50 per cent. The number of cases in China – more than 83,700 – still trails that of the US, which has more than 679,000.

Addressing reporters later on Friday, Trump doubled down on his assertion, stating that China had the most deaths in the world.

“We don’t have the most in the world – deaths,” Trump said of the US tally, which stands at more than 34,000. “The most in the world has to be China. It’s a massive country. It’s gone through a tremendous problem with this.”

Pompeo’s statement highlights an outlier theory that the coronavirus did not come from a Wuhan wildlife market as originally postulated, but from a laboratory in that city.

The Washington Post reported on Tuesday that US officials who had visited the Wuhan Institute of Virology sent diplomatic cables to Washington as early as January 2018 warning about safety and management weaknesses at the lab, and stated outright that the facility’s work on bat coronaviruses created a pandemic risk.

Experts have overwhelmingly said analysis of the coronavirus’s genome rules out the possibility that it was engineered by humans, nor is it likely that it emerged from a negligent laboratory in Wuhan.

But Trump gave the theory a boost at Friday’s press briefing, saying that “it seems to make sense” and said it was a matter of active investigation within his administration.

“We’re going to find out,” he said. “All I can say is: wherever it came from it came from China.”

Taking questions later in the briefing, top US health official Anthony Fauci dismissed suggestions that the virus had been engineered, but did not weigh in on how it might have begun to spread.

“There was a study recently that we can make available to you where a group of highly qualified evolutionary virologists look at the sequences there and the sequences in bats as they evolve, and the mutations that it took to get to the point where it is now is totally consistent with a jump of a species from an animal to human,” Fauci, director of the National Institute of Allergy and Infectious Diseases, said.

In February, a Chinese study by researchers at Xishuangbanna Tropical Botanical Garden, under the Chinese Academy of Sciences and the Chinese Institute for Brain Research, determined that the coronavirus was introduced outside the wet market.

China has consistently denied any connection between the laboratory and the virus and on Thursday reiterated their stance with Foreign Ministry spokesman Zhao Lijian saying: “China believes the origin of the virus is a scientific issue that has to be seriously handled.

“The World Health Organisation said there is no evidence proving that it is made in a lab. And many renowned medical experts have also said that the claim that the virus leaked from a lab has no scientific basis.”

Tensions continue to rise between the two countries, in the wake of Trump’s decision to halt funding from the World Health Organisation over what he said was its bias in favour of China.

In 2015, the Wuhan Institute of Virology became China’s first laboratory designated as BSL-4, meaning it has the highest level of international bioresearch safety.

On Wednesday, Trump announced that he was investigating the role of the laboratory in the outbreak, and had discussed the link between the Covid-19 pandemic and the virology lab on a phone call with China’s President Xi Jinping.

Pompeo said on Thursday he blames China for what he says is a lack of information.

“It’s very clear now that the Chinese Communist Party and the World Health Organisation didn’t put that information out into the international space as they’re required to do in a timely fashion, and the result of that is that we now have this global pandemic,” he said on Friday.

“The Chinese Communist Party needs to come clean about what took place there, so the whole world can see.”