World Health Organization officials said Friday they were particularly concerned with the appearance of coronavirus cases in several countries, in which it is unclear how the patients were infected.

“Although the total number of cases outside Flag of China remains relatively small, we are concerned about the number of cases with no clear epidemiological link, such as travel history to Flag of China or contact with a confirmed case,” said WHO Director General Tedros Adhanom Ghebreyesus.

Health officials are focused on determining whether instances of local transmission have occurred and where — because that would indicate containment is not working and that the outbreak is instead spreading geographically.

Apart from the Diamond Princess cruise ship where local transmissions occured, South Korea now has the most cases outside China, and WHO officials said they’re working with the Korean government to understand the exact transmission dynamics that caused that increase.

Iran is another hotspot WHO officials said they are focused on. In three days, Iran has gone from zero cases to 18 cases and four deaths. The WHO has supplied testing kits and said it plans to provide further support to Iran in coming days.

But the biggest concern, WHO officials said, continues to be the possible spread of the coronavirus to developing countries with weaker health systems that are ill-equipped to handle such an epidemic.

Because of that, Tedros said he would be meeting with African health ministers on Saturday to talk about their preparation efforts.