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.
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.