“Of course we can have concerns and worries, it’s understandable, but let’s really calm down and do the right things, and use the window of opportunity to contain this outbreak,” he said.

He added, without identifying countries, that “in some places we are not seeing the level of response that we expected.” For that reason, he said, the W.H.O. was reminding the world “that the window of opportunity is narrowing and that we still have to do our best to catch up.”

Dr. Tedros said there were “positive signals” that nations could contain the virus, such as the dozens of countries with fewer than 100 cases. He also cited the slowdown of infections in China as a sign that the virus could be contained.

“There is a point in any epidemic where you believe you can no longer contain the virus, or like it was influenza and you have to shift your resources to saving lives,” said Dr. Michael Ryan, the executive director of the W.H.O.’s health emergencies program. “Now W.H.O. does not believe that we’re there yet.”

Coronavirus kills an adviser to Iran’s Ayatollah Khamenei.

An adviser to Iran’s supreme leader died from coronavirus illness on Monday, state media reported — the first fatality of a top Iranian official from the scourge that has hit the country especially hard and made it a hub of contagion in the Middle East.

The adviser, Mohammad Mirmohammadi, 71, is a member of the Expediency Council, which provides advice to the supreme leader, Ayatollah Ali Khamenei, 80. It was unclear from state media accounts whether Mr. Mirmohammadi, who died at a Tehran hospital, had been in direct contact with Ayatollah Khamenei when he was contagious.

The state media accounts also said Mr. Mirmohammadi’s mother had died in recent days from the coronavirus and an uncle — his mother’s brother — was being monitored in quarantine for possible infection.