The US welcomes the World Health Organization's probe into the origins of the novel coronavirus in China, its ambassador to the United Nations in Geneva said Friday.

"We welcome the WHO's investigation. We view the scientific investigation as a necessary step to having a complete and transparent understanding of how this virus has spread throughout the world," ambassador Andrew Bremberg told reporters.

It was an unexpected endorsement, given that the WHO has faced fierce US criticism over its handling of the coronavirus crisis.

Earlier Friday, an epidemiologist and an animal health specialist from the WHO left for China to try and identify the animal source of the new coronavirus pandemic.

The WHO said the advance team would be in Beijing for the weekend as they lay the groundwork for a wider mission aimed at identifying how the virus jumped from animal to humans.

Bremberg said the US expected the Chinese authorities "will offer the team of scientists full access to data, samples and localities, and look forward to its timely report".

US President Donald Trump has accused the WHO of botching its handling of the pandemic and of being a "puppet of China".

On Tuesday the United States formally started its withdrawal from the WHO, making good on Trump's threats to deprive the UN body of its top donor over its management of the pandemic.

The WHO launched an independent panel Thursday to review its response to the pandemic.

The novel coronavirus has killed at least 556,000 people and infected more than 12.4 million since it emerged in China last December.

Scientists believe the killer virus originated from a market in the city of Wuhan selling exotic animals for meat.