Speaking in Geneva, a WHO expert on viruses originating in animals said the evidence pointed to bats as the primary source, with another animal acting as an intermediate host.

The organisation also repeated that it had not seen any evidence, cited by US President Donald Trump, that the virus could have originated in a Chinese laboratory.

Scientists aren’t sure where exactly the outbreak began. Evidence points to a market in the Chinese city of Wuhan, but of 41 early cases of the virus, only 27 had a direct connection to the market, reports the BBC's Geneva correspondent Imogen Foulkes.

The virus will have jumped from bats to another animal before infecting humans, but which animal remains unclear.

When the Middle East Respiratory Virus, or Mers, emerged in 2012, it took a year to discover the origin in camels.

Asked last week if there was any foundation in the US claims that the virus emerged from a laboratory, the WHO said that after reviewing evidence from multiple scientists, it was assured the outbreak was natural in origin.