US President Joe Biden has asked intelligence officers to "redouble" their efforts to find out the true origin of the COVID-19 outbreak.
An international team of World Health Organisation scientists, working with experts in China, had been researching how the pandemic began, and as part of its work, visited the province of Wuhan where the first cases were reported.
The team was accompanied by Chinese officials at all times, but did speak to patients, first responders and local scientists, and in the end concluded the novel coronavirus most probably jumped from animals to humans.
Another unlikely theory is that it may have originated in a laboratory accident.
However on Wednesday, Mr Biden said he did not feel there had been sufficient information to determine exactly where the coronavirus had come from, and he has now asked a team of intelligence officers to investigate again.
He has also asked for more "specific questions" to be asked of China.