The World Health Organization said on Tuesday urged countries to investigate any suspicious early cases of COVID-19, after French scientists said a man may have been infected with the disease as early as December 27.

The case points to the presence of COVID-19 in France nearly a month before the French government confirmed its first cases.

"This gives a whole new picture on everything," WHO spokesman Christian Lindmeier told a U.N. briefing in Geneva, referring to the French report.

"The findings help to better understand the potential virus circulation of COVID-19," he added, saying other earlier cases could emerge after retesting samples.

The latest remarks by Lindmeier come as the number of COVID-19 infections worldwide exceeded 3.6 million, with the death toll going beyond 253,000.

As the war against the disease continues, world leaders on Monday pledged some €7.4 billion towards research into a possible vaccine and treatments.

The pledges were made at a European Commission-hosted pledging conference attended via videoconference by leaders from at least 40 countries around the world.

In a briefing on Monday, WHO Director-General Tedros Adhanom urged the world to unite in the fight agsinst COVID-19, confirming the agency’s focus was shifting towards this search for a remedy.

"This virus will be with us for a long time, and we must come together to develop and share the tools to defeat it," he said.