The World Health Organization (WHO) called on Friday for an audit of Chinese laboratories where the first cases of COVID-19 were identified as part of the investigation into the origin of the pandemic.
WHO chief Dr Tedros Adhanom Ghebreyesus proposed the audit during a meeting with the organization's member states.
He said that to move the probe forward it was necessary to carry out "controls of relevant laboratories and research institutions active in the region where the first human cases were identified in December 2019".
The first infections were detected in Wuhan, a Chinese city in the central Hubei province.
Ghebreyesus's demand comes a day after he said it was premature to rule out a potential link between the pandemic and a laboratory leak.
He also urged China to be more transparent, flagging that getting access to raw data had been a challenge for the international team that travelled to the country earlier this year to investigate the source of COVID-19.
"We expect China to support this new phase of the scientific process by sharing all relevant data in a spirit of transparency. Similarly, we expect all Member States to support the scientific process by refraining from politicising it," Ghebreyesus said Friday.
In addition to the Chinese laboratory controls, WHO also wants to conduct "integrated studies of humans, wildlife, captive and farmed animals, and the environment" and "studies that prioritise geographical areas where SARS-CoV-2 circulation has been reported earliest and adjacent areas where there has been a high prevalence of SARS-related coronavirus (SARSr-CoV) in non-human reservoirs".
The agency also calls for "studies related to animal markets in and around Wuhan, including ongoing studies of animals sold at the Huanan wholesale market", as well as "studies related to animal tracing activities, with additional work in epidemiology and molecular epidemiology, including early virus sequences".
The new phase of the study, however, is shaping up to be tricky. Beijing on Friday rejected the WHO chief's criticism of China's alleged lack of cooperation. It previously described theories that the virus may have escaped from a Wuhan laboratory as "absurd".
It has also suggested the virus may not have originated in China, promoting theories that it may have been imported into the country on frozen seafood.
The team of WHO experts mandated to investigate the origin of the pandemic visited China in January after months of diplomatic back-and-forth. It concluded that the virus had probably been transmitted from bats to humans via another animal.