The World Health Organisation (WHO) says an investigation into whether covid originated from an accident at a Chinese laboratory was "not extensive enough".
Global health leaders have said that all hypotheses into the origins of covid-19 'remain on the table' and more research will be tested.
Some of the research will look into if the virus could have entered the human population as a result of a laboratory leak.
Th World Health Organisation (WHO) said that "no stone will be left unturned" as it continues its probe into where the virus came from.
The comments come as the team investigating the virus publish an initial report.
China has faced claims that the Wuhan Institute of Virology could be the suspected source of the Covid-19 virus.
The WHO and China said in February the virus which causes Covid-19 - SarS-CoV-2 is "extremely unlikely" to have entered the human population as a result of a laboratory-related incident.
But as the report was published, Dr Tedros Adhanom Ghebreyesus, director general of the WHO, said: "The team visited several laboratories in Wuhan and considered the possibility that the virus entered the human population as a result of a laboratory incident.
"However, I do not believe that this assessment was extensive enough.
"Further data and studies will 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.
"Let me say clearly that as far as WHO is concerned all hypotheses remain on the table."
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The report concluded that the introduction of the virus from an intermediate host is the most likely scenario - which means the virus "jumped" from one species to another, and then jumped from the second species to humans.
It also suggests that the virus was circulating for several weeks before it was initially detected.
Dr Tedros added: "This report is a very important beginning, but it is not the end. We have not yet found the source of the virus, and we must continue to follow the science and leave no stone unturned as we do.
"Finding the origin of a virus takes time and we owe it to the world to find the source so we can collectively take steps to reduce the risk of this happening again. No single research trip can provide all the answers."
Since the virus was first detected in December 2019, there have been more than 127 million cases around the globe and 2.8 million deaths.
