"We need to continue to push until we get the answer," Tedros Adhanom Ghebreyesus told reporters, referring to the search for the origins of the virus that first surfaced in China in late 2019.

Solving the mystery of where the SARS CoV-2 virus came from and how it began spreading among humans is viewed as vital to averting future pandemics.

The two main theories that have been hotly debated have centred on the virus naturally spilling over from bats to an intermediary animal and into humans, or escaping due to a lab accident.

But an article on the Nature website Tuesday suggested that the WHO has "quietly shelved the second phase of its much-anticipated scientific investigation into the origins of the Covid-19 pandemic".

It quoted Maria Van Kerkhove, the WHO expert leading the agency's Covid response, saying that "there is no phase two".

The WHO planned for work to be done in phases, she told the report, but "that plan has changed", adding that "The politics across the world of this really hampered progress on understanding the origins".

Van Kerkhove responded angrily Wednesday when asked about the article, attributing the interpretation that WHO had shelved its origins search to "an error in reporting, which is really quite concerning because it's causing some headlines that are inaccurate".

"WHO has not abandoned studying the origins of Covid-19, we have not and we will not," she said.

The WHO carried out a first phase of investigation by sending a team of international experts to Wuhan, China, in January 2021 to produce a first phase report, written in conjunction with their Chinese counterparts.

While the initial plan had been to send a second team, Van Kerkhove said the WHO had shifted tactics and decided instead to create a team of scientists with an expanded scope to investigate new pathogens and study how to prevent future pandemics, while continuing to probe Covid-19's origins.

The Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) was created "to conduct an independent assessment of the origins of Covid-19, but also to work more broadly to establish a framework to understand the origins of any future epidemic and pandemic pathogen, and the origins in which it emerges," Van Kerkhove said.

"We will continue to ask for countries to depoliticise this work, but we need cooperation from our colleagues in China to advance this," she said.

Tedros said there were two reasons for not abandoning the origins search.

The first was scientific, he said: "We need to know how this started in order to prevent the next one."

"The second (is) moral: millions of people lost their lives, and many suffered, and the whole world was taken hostage by a virus."

"It's morally very important to know how we lost our loved ones."