In what could be seen as a warning to countries currently easing their lockdowns, the World Health Organization (WHO) warned that the “worst is yet ahead of us” in the coronavirus outbreak — asking for cooperation and global solidarity.

The WHO Director-General Tedros Adhanom Ghebreyesus didn’t specify why he believes the outbreak that has infected some 2.5 million people and killed over 166,000 could get worse. In the past, he had warned over the spread of the virus in Africa, with a less developed health system.

“Trust us. The worst is yet ahead of us,” Tedros told reporters from WHO headquarters in Geneva. “Let’s prevent this tragedy. It’s a virus that many people still don’t understand.”

Tedros compared the virus to the 1918 flu that killed 675,000 people in the US and tens of millions of people around the world. But he argued that the world now has the technology to prevent “that kind of crisis”.

The WHO has been on the defensive after President Donald Trump — the WHO’s biggest single donor — last week ordered a halt to U.S. funding for the agency, alleging that it botched the early response to the outbreak.

Trump insisted WHO had failed to adequately share “in a timely and transparent” way information about the outbreak after it erupted in China late last year. Nevertheless, Tredros said: “There is no secret in WHO because keeping things confidential or secret is dangerous.”

Tedros said U.S. Centers for Disease Control and Prevention staffers have been seconded to work with his agency, suggesting that was a sign of WHO’s transparency. “Having CDC staff (at WHO) means there is nothing hidden from the U.S. from day one,” Tedros said.

Some Asian and European governments have gradually eased or started relaxing “lockdown” measures like quarantines, school and business closures, and restrictions on public gatherings, citing a decline in the growth of COVID-19 case counts and deaths.

Germany reopened many of its shops this week and some of its schools from May 4. But strict curbs on social contact will remain in place and Germans will be encouraged to wear masks in shops and on public transport. Chancellor Angela Merkel said the country had achieved “interim success” in slowing the spread of the virus.

Meanwhile, France will unveil within two weeks a plan to progressively lift restrictions on travel and business that aim to curb the coronavirus epidemic, Prime Minister Edouard Philippe said.

In the US, Trump has urged governors to reopen their states despite experts’ warnings that doing so too soon would provoke a devastating resurgence of the virus. Dr. Anthony Fauci, the country’s leading infectious-disease expert, has said a vaccine is at least a year to 18 months away.