Hong Kong CNN  — 

It was supposed to offer insight into the origins of the Covid-19 pandemic. But since its release on Tuesday, the long-awaited World Health Organization investigation has drawn criticism from governments around the world over accusations it is incomplete and lacks transparency.

In a joint statement, the United States and 13 other governments, including the United Kingdom, Australia and South Korea, expressed concerns over the study’s limited access to “complete, original data and samples.”

The European Union issued its own statement, expressing the same concerns in slightly softer language. The criticism follows an admission from WHO Director-General Tedros Adhanom Ghebreyesus, that investigators faced problems during their four-week mission to the central Chinese city of Wuhan, where the coronavirus was first detected in December 2019.

In a news briefing Tuesday, Tedros appeared to contradict the study’s central findings by suggesting the theory that the virus escaped from a Wuhan laboratory should be followed up – even though the report noted such a possibility was “extremely unlikely” and did not recommend further research on the hypothesis.

The WHO investigation, conducted more than a year after the initial outbreak, came under intense scrutiny from the outset. Some scientists and the US government have questioned the independence and credibility of the study, raising concerns over Chinese government influence. Beijing, meanwhile, has accused Washington and others of “politicizing” the origin of the virus.

After repeated delays, the WHO report, compiled by a team of international experts and their Chinese counterparts, was finally released on Tuesday. It provides a detailed examination of the data collected by Chinese scientists and authorities from the early days of the pandemic, but offers little new insight or concrete findings on where and how the virus spread to humans.

China has vehemently rejected any criticism or blame related to its handling of the pandemic.

The Chinese Foreign Ministry said in a statement Tuesday that China has always been “a supporter for global scientific research on the source of the virus and its transmission routes.”

“The Chinese side offered necessary facilitation for the team’s work, fully demonstrating its openness, transparency and responsible attitude,” the statement said, adding the study of origins should also be conducted in other countries.

Tuesday’s joint statement, signed by the US and its allies, recognized the WHO experts’ “tireless work” to understand how the pandemic started, but also raised questions over the timing and independence of the report.

“It is equally essential that we voice our shared concerns that the international expert study on the source of the SARS-CoV-2 virus was significantly delayed and lacked access to complete, original data and samples.”

The public rebuke from the US and others further highlights the difficulty of conducting transparent and independent scientific research into the origins of the virus, which has infected more than 128 million people and killed over 2.8 million worldwide, according to Johns Hopkins University data.

WHO Director-General Tedros Adhanom Ghebreyesus said the WHO team encountered difficulties in accessing raw data during their visit to Wuhan.

Data access

Speaking in the briefing Tuesday, WHO chief Tedros conceded the international experts faced problems with data access in Wuhan.

“In my discussions with the team, they expressed the difficulties they encountered in accessing raw data. I expect future collaborative studies to include more timely and comprehensive data sharing,” said Tedros, who had previously faced criticism that his agency was too close to China.

Dominic Dwyer, an Australian infectious diseases expert and member of the WHO team, told Reuters last month the team had requested raw patient data on the 174 early cases in Wuhan in December 2019, but was refused and provided only with a summary instead.

In its own statement, the EU said the report was a “helpful first step,” but it regretted “the late start of the study, the delayed deployment of the experts and the limited availability of early samples and related data.”

“Only through a thorough review of the origins of the virus and its transmission into the human population, will we be able to better understand and control this pandemic, and to better prevent and prepare for future health emergencies,” the statement said.

In comparison, the response from the US government was much more direct and strongly-worded.

“The report lacks crucial data, information and data access – and represents a partial, incomplete picture,” White House Press Secretary Jen Psaki said at a briefing.

She said Chinese authorities “have not been transparent, have not provided underlying data – that certainly does not qualify as cooperation.”

“[The report] doesn’t lead us to any closer of an understanding or greater knowledge than we had six to nine months ago about the origin,” she said.

Security guards stand in front of the closed Huanan Seafood Wholesale Market in the city of Wuhan, in the Hubei Province, on January 11, 2020.

‘Political hurdle’

The report examines four possible ways the coronavirus could have emerged, and concludes that it is most likely to have spread to humans from an intermediate animal host – a belief long held by scientists. But it did not answer crucial questions on how that transmission happened.

It recommends further studies to trace the animals sold at markets in and around Wuhan, including interviewing workers at wildlife farms and testing them for coronavirus antibodies.

The report also says it is “extremely unlikely” the virus leaked from a laboratory incident – a theory promoted by the previous Trump administration and fiercely denied by the Chinese government.

“We just found no really tangible evidence or real leads on that, despite asking a lot of quite hard questions that were asked to the Wuhan Institute of Virology,” Dr. Peter Daszak, a member of the WHO team of experts who visited Wuhan, told CNN.

“They tested all of the staff in the bat coronavirus group for coronaviruses, for SARS-CoV-2, to see if they’d been infected, and they were negative,” he said.

But critics say the report has failed to provide concrete evidence to dismiss that possibility.

On Tuesday, WHO head Tedros said the report’s assessment on the lab leak theory was not “extensive enough,” and further data and studies would be needed to reach more robust conclusions.

“Although the team has concluded that a laboratory leak is the least likely hypothesis, this requires further investigation, potentially with additional missions involving specialist experts, which I am ready to deploy,” Tedros said.

Peter Ben Embarek, the lead investigator for the WHO mission, told the briefing the report was “only the start,” admitting “we’ve only scratched the surface of these very complex set of studies that need to be conducted.”

The report makes a series of recommendations for further studies, including testing for for coronavirus antibodies in samples collected through blood banks prior to the Wuhan outbreak.

Daszak said there was currently no plan set for the WHO mission to return to China to conduct further studies.

“The understanding (is) that the next phase of this work will be to follow those recommendations and begin those studies, and we’re already talking to the China side about our next steps and how we can help that happen,” he said.

But some analysts warned concerns that have overshadowed the WHO study could haunt future research, especially as relations deteriorate between China and Western countries.

“The thing is that you won’t avoid politics,” said Yanzhong Huang, a senior fellow for global health at the US based Council on Foreign Relations.

Huang said he did not expect the investigation to be transparent, WHO to play an independent leadership role, or China to be fully cooperative in the probe as long as a “political hurdle” remained.

CNN’s Sandi Sidhu contributed reporting.