"The conclusion that a laboratory leak is extremely unlikely was reached by the China-WHO joint expert team based on field visits to relevant laboratories in Wuhan," foreign ministry spokeswoman Mao Ning said.

"This has been widely recognised by the international community and the scientific community," she added.

The CIA said Saturday the virus was "more likely" leaked from a Chinese lab than transmitted by animals.

The new assessment came after John Ratcliffe was confirmed last week as the CIA director under the second White House administration of Donald Trump.

"CIA assesses with low confidence that a research-related origin of the Covid-19 pandemic is more likely than a natural origin based on the available body of reporting," a CIA spokesperson said in a statement Saturday.

The agency had not previously made any determination on whether Covid had been unleashed by a laboratory mishap or spilled over from animals.

Beijing on Monday urged the United States to "stop politicising and instrumentalising the issue of origin-tracing".

Mao said Washington should "stop smearing and shifting the blame to other countries (and) should respond to the legitimate concerns of the international community as soon as possible".