A leading scientist on the WHO's COVID-19 mission to China said on Tuesday that a follow-up trip could be helpful to gather additional research on the origins of the disease, but should be separate from any audit of information provided by Beijing.

The comments from Dutch virologist Marion Koopmans came after the United States called on Tuesday for international experts to be allowed to evaluate the source of the coronavirus and the early days of the outbreak in a second phase of the WHO's investigation into the origins of the coronavirus. 

Koopmans was part of the WHO-led team which spent four weeks in China earlier this year and in March published a report jointly with Chinese scientists that said the virus had probably been transmitted from bats to humans through another animal.

"Introduction through a laboratory incident was considered to be an extremely unlikely pathway," its report said.