GENEVA: A two-member advance team of World Health Organization (WHO) experts has left for China to organise an investigation into the origins of the novel coronavirus behind a pandemic that has killed more than 550,000 people globally, the UN agency said on Friday.

The virus is believed to have emerged in a wholesale market in the central Chinese city of Wuhan late last year after jumping the species barrier from the animal kingdom to infect humans.

The two WHO experts, specialists in animal health and epidemiology, will work with Chinese scientists to determine the scope and itinerary of the investigation, WHO spokeswoman Margaret Harris said, declining to name them.

“We know it’s very, very similar to the virus in the bat, but did it go through an intermediate species? This is a question we all need answered,” Harris told a news briefing.

WHO director-general Tedros Adhanom Ghebreyesus later told a news conference: “Two WHO experts are currently en route to China to meet with fellow scientists and learn about the progress made in understanding the animal reservoir for COVID-19 and how the disease jumped between animals and humans.”

He added, “This will help lay the groundwork for the WHO-led international mission into the origins.”

COVID-19 is the respiratory disease caused by the virus.

The United States, the WHO’s largest WHO donor, this week notified the agency that it was withdrawing in a year’s time after accusing it of being too close to China and not doing enough to question Beijing’s actions at the start of the crisis.

“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,” Andrew Bremberg, U.S. ambassador to the United Nations in Geneva, said in a statement to Reuters.

“We expect that the CCP (Chinese Communist Party) will offer the team of scientists full access to data, samples, and localities, and look forward to its timely report,” Bremberg said.

U.S. President Donald Trump and Secretary of State Mike Pompeo have said the pathogen may have originated in a laboratory in Wuhan, although they have presented no evidence for this and China has denied it. Scientists and U.S. intelligence agencies have said it emerged in nature.