A WHO-led team that spent four weeks in and around Wuhan in January and February with Chinese researchers said in a report in March that the virus had probably been transmitted from bats to humans through another animal, and that “introduction through a laboratory incident was considered to be an extremely unlikely pathway.”

U.S. President Joe Biden ordered aides to find answers to the origin of the virus that causes COVID-19, saying on Wednesday that U.S. intelligence agencies are pursuing rival theories potentially including the possibility of a laboratory accident in China.

The initial WHO study was “insufficient and inconclusive,” the U.S. mission to the U.N. in Geneva said in a statement on Thursday, calling for what it called a timely, transparent and evidence-based second probe to be conducted, including in China.

“It is critical that China provides independent experts full access to complete, original data and samples relevant to understanding the source of the virus and the early stages of the pandemic,” the U.S. statement said.

China, through remarks by a representative at its embassy in the United States, said on Thursday it supported “a comprehensive study of all early cases of COVID-19 found worldwide and a thorough investigation into some secretive bases and biological laboratories all over the world.”

Simon Manley, Britain’s ambassador to the U.N. in Geneva, said in a separate statement: “Phase one of the WHO-convened COVID-19 origins study was always meant to be the beginning of the process, not the end. We call for a timely, transparent, evidence-based, and expert-led phase two study, including in the People’s Republic of China, as recommended by the experts’ report.”

Mike Ryan, WHO’s top emergency expert, told its annual meeting of health ministers on Wednesday: “We’ve had consultations informally with many member states to look at what happens in the next phase. And we will continue to have those discussions in the coming weeks.”

(Reporting by Stephanie Nebehay in Geneva Editing by Chris Reese and Matthew Lewis)