The World Health Organization said Monday that Washington had provided no evidence to support "speculative" claims by the US president that the new coronavirus originated in a Chinese lab.
"We have not received any data or specific evidence from the United States government relating to the purported origin of the virus -- so from our perspective, this remains speculative," WHO emergencies director Michael Ryan told a virtual briefing.
Scientists believe the killer virus jumped from animals to humans, emerging in China late last year, possibly from a market in Wuhan selling exotic animals for meat.
But US President Donald Trump, increasingly critical of China's management of the first outbreak, claims to have proof it started in a Wuhan laboratory.
And US Secretary of State Mike Pompeo on Sunday said "enormous evidence" backed up that claim, which China has vehemently denied.
"Like any evidence-based organization, we would be very willing to receive any information that purports to the origin of the virus," Ryan said, stressing that this was "a very important piece of public health information for future control.
"If that data and evidence is available, then it will be for the United States government to decide whether and when it can be shared, but it is difficult for the WHO to operate in an information vacuum in that regard," he added.
The UN agency also hails the fundraising efforts of a teleconference of world leaders to boost development of a coronavirus vaccine, but warns that the money raised would only cover part of the ongoing response against the pandemic saying "this virus will be with us for a long time".