Beijing has barred the entry of a 10-member World Health Organization team investigating the origins of the coronavirus pandemic after their visas were not approved.

Tedros Adhanom Ghebreyesus, WHO director-general, said on Tuesday that he was “very disappointed” after China blocked the arrival of the virologists.

“Two members [of the team] had already begun their journeys and others were not able to travel at the last minute,” Mr Tedros said.

He added that the WHO had been in contact with Chinese officials who said they would expedite the visa approval procedure. More than 86m people have been infected worldwide by coronavirus, which has claimed more than 1.8m lives.

The slow progress of the WHO probe and its lack of access into the origins of the pandemic have drawn criticism from the US and calls for greater transparency from some western governments.

President Donald Trump has threatened to suspend US funding to the WHO and withdraw from the global health agency after accusing it of “mismanaging” the pandemic.

Huang Yanzhong, a senior fellow for global health at the Council on Foreign Relations in New York, said: “This is certainly a bad omen for the upcoming WHO investigation in China. It’s not like the arrival was unexpected.”

He added that the WHO’s rare public criticism of China may help bolster the organisation’s international credibility and its leverage over Beijing when negotiating for access, as happened during a 2003 probe into the origins of the Sars outbreak.

China maintains that it welcomes the investigation, which will be primary focused on identifying when, where and how the Sars-Cov-2 virus that causes Covid-19 made the jump from animals to humans.

“Tracing the source [of the virus] is a complicated issue. To ensure that the international team’s work progresses smoothly, they must go through the necessary procedures, ” Hua Chunying, a Chinese foreign ministry spokesperson, said on Wednesday in response to questions about the delay.

Many scientists believe the disease originated in bats, which have been found to carry genetically similar virus strains. But many stages in the virus’s transmission to humans remain uncharted.

A leading theory, which suggested that the first human infections came from a market in Wuhan where multiple species of wildlife were on sale, has been drawn into question after several early cases were discovered without an obvious link to the location.

Despite uncertainty over the exact transmission route, WHO experts have maintained that the investigation must begin in Wuhan and follow the evidence from studies conducted in the central Chinese city.

Chinese officials, however, have consistently suggested that the origin of the virus is outside the country. The country’s state media has also marshalled fringe theories and selectively reported international research to argue that the virus began elsewhere and only arrived later in Wuhan, possibly via cold chain goods.

Over the weekend, Wang Yi, the Chinese foreign minister, declared that “more and more research suggests that the pandemic was likely to have been caused by separate outbreaks in multiple places in the world”.

Concerns over the WHO team’s ability to carry out a scientifically rigorous and independent set of studies mounted after a two-person advanced team failed to visit Wuhan in July.

Washington renewed calls for transparency after terms of reference for the probe released in November stated that experts would “augment, rather than duplicate” studies already carried out by China. Additional reporting by Xinning Liu in Beijing