At least one child has died of unexplained liver inflammation in a growing international outbreak of puzzling hepatitis cases in children, according to the World Health Organization.

The outbreak tally has reached more than 170 cases in 12 countries and is expected to continue growing. At least 17 children—10 percent of the cases—have required liver transplants. The ages of the affected children range from one month to 16 years, though the majority are children younger than 10 and many younger than 5.

Over the weekend, the WHO reported 114 cases in the United Kingdom, 13 in Spain, 12 in Israel, six in Denmark, fewer than five in Ireland, four in the Netherlands, four in Italy, two in Norway, two in France, one in Romania, and one in Belgium. The WHO also noted nine cases in the US, all in Alabama. But two additional cases were reported in North Carolina last week, bringing the US total to at least 11. Two of the US cases resulted in transplants.