US President Joe Biden has ordered intelligence agencies to investigate the emergence of Covid-19, amid growing controversy about the virus's origins.
In a statement, Mr Biden asked US intelligence groups to "redouble their efforts" and report to him within 90 days.Covid-19 was first detected in the Chinese city of Wuhan in late 2019.
More than 168 million cases have since been confirmed worldwide and at least 3.5 million deaths reported.
Authorities linked early Covid cases to a seafood market in Wuhan, and scientists believed the virus first passed to humans from animals.
But recent US media reports suggest growing evidence the virus could instead have emerged from a laboratory in China.
Beijing has condemned the reports and suggested it could have come from a US laboratory instead.