Microwave radiation that is “directed” is the likely cause of illnesses among American diplomats in Cuba and China, a new report by a committee of the US National Academy of Sciences has found.

The study commissioned by the US State Department and released on Saturday is the latest attempt to find a cause for the mysterious illnesses that started to emerge in late 2016 among US personnel in Havana.

The study found that “directed, pulsed radio frequency energy appears to be the most plausible” explanation for symptoms that included intense head pressure, dizziness and cognitive difficulties.

It found this explanation was more likely than other previously considered causes such as tropical disease or psychological issues.